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Ch.B., M.D.S. (Birm.), L.D.S. (Eng.) 






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When this work was commenced nearly six years ago, 
a " plan of campaign " was drawn up to which it was 
decided to adhere, and to continue the work until the 
whole field had been covered, or at least investigated 
to some extent. It was further decided to publish nothing 
until the chain of evidence was more or less complete. 
This has obvious disadvantages, one of which is the 
length to which the subject has grown, and another the 
fact that in several matters the results have been fore- 
stalled in publication by others working along similar 
lines. The work, like all work, is still incomplete, but 
sufficiently important conclusions have been reached, 
I think, to justify publication. 

The present volume is an amplified form of lectures 
which have been delivered in this University to Medical 
Practitioners and to Medical and Dental Students. 

H. P. P. 

University of Otago, N.Z. 
November, 191 1. 









VI. THE ODONTOGRAPH - - - - - 60 





XI. THE SALIVA ------ 12$ 






ORGANISMS ----- 234 





INDEX ------ 298 




















TEETH - - - - - 58 


19. ODONTOGRAPH - - - - - - 6l 



22. ODONTOGRAMS." MAORI - - - - -63 



25. ODONTOGRAMS : DOG'S TEETH - - - "65 








LIGHT - - - - - 7: 


LIGHT - - - - - - J2 






RFACE PRISMS - - - - - 82 

40. SURFACE PRE - ... 8$ 

41. CALCARINE FISSURES - - - - - 84 

42. SINUOUS FISSURES - - - - 85 








50. SCLEROMETER - - - - - - 102 

51. SEGREGATOR - - - - - ~ I 33 

52. chart: acid dietary - 149 

53. mucinometer ------ 185 

54. epithelial cell in saliva - - - - 1 92 

55. portions of the crown after subjection to fer- 

mentation ------ 208 

56. toothbrush ------ 221 



LATION - - - - - -I36 


BISCUIT __.--- I4 2 



FRICES - - - - - 151 

IZING THE TONGUE - - - - -1^4 




XI. CHLORIDES - - - - - - I So 

XII. MUCIN - - - - - 184 


Page 129, line 11, for "day," read "dog." 

Page 144, Table III., for "citric acid 7 per cent.," read "1 per 
cent ," and for " tartaric acid 7 per cent," read " 1 per cent." 

Page 183, line 14, for "lobes," read "bolus"; line 15, for "are," 
read "is." 

Page 184, Table XII., for " Sugar, 6'i35 " read " o - i35." 


Nearly one hundred years ago Fox wrote, as regards 
the prevention of dental caries, that " this delightful 
secret, although it is pretended to in the" advertisement 
of every quack, we can only expect to acquire when the 
philosopher's stone and the grand panacea have been 
obtained." If this somewhat prophetic utterance is 
to be fulfilled, there would not seem to be any reasonable 
hope that the prevention of dental caries can yet be 
regarded as within the limits of practicability. 

There is no doubt, though, that the disease has become 
much more serious in its proportions since Fox's time, 
and the attitude of fatalism towards it is no longer 
justifiable and is not consonant with our modern know- 
ledge of pathology and the means of immunity. 

The general plan of the present work has been to 
inquire into past methods of the preventive treatment 
of dental caries, to compare these with present methods, 
and to collect data as to the incidence of caries in various 
nations and in various stages of civilization. 

A critical examination of the powers of passive 
resistance on the part of the teeth has been carried out, 
together with an investigation of the forces of active 
natural protection, and a consideration of the means 


whereby both passive and active resistance might be 
fortified against the attacks of the oxygenetic or acid- 
forming forces as constituted in the combination of 
carbohydrates with organisms, and a further considera- 
tion of how these latter forces might be weakened or 
destroyed entirely. 

^The dietaries of " natural " and civilized peoples have 
been examined in detail, and inference from the one and 
corrections for the other have been made. 

Finally, educational and legislative methods of deal- 
ing with the problem have been suggested. 

The author is convinced that, by the means and methods 
subsequently to be described, not only may the occurrence 
of caries be prevented, but in some cases actually " cured." 

In several patients (children) who have been under 
constant observation during the past two years, and in whom 
caries was commencing, not only have no more carious 
cavities appeared, but those that were present have not 
progressed, and the surface has become quite hard. The 
condition which is known as " arrested caries " has, in 
fact, been established. [This, despite the fact that tooth- 
brushes have been used only quite spasmodically.'] 
" Green stain " was well established in one case, but 
now, with no other treatment, has practically disappeared. 

The significance of this will be at once appreciated in 
connection with measures to be adopted for the arrest of the 
alarmingly increasing tide of carious disease, especially 
in children attending' elementary schools. 




The records of the practice of dentistry chiefly by 
medical means date back in the case of the Egyptians 
to somewhere about three thousand years before the 
Christian era. Even at this early period we have 
some evidence that methods were in vogue for the pre- 
vention of dental disease. For instance, the " Ebers " 
papyrus, probably compiled gradually from 3000 B.C. 
to 1550 B.C., contains prescriptions for " strengthening 
the teeth," of which the following is an example : 

Powder of flint stones ' . . . . part i. 

Green lead . . . . . . . . part i. 

Honey . . . . . . . . part i. 

To be rubbed on the teeth. 

This might now be classified as an antiseptic and 
abrasive tooth-paste. 

Records of Chinese medicine written about the same 
time as the above, and translated by Dabry, give pre- 
scriptions for whitening the teeth, and for a powder to 
prevent the progress of caries, the chief ingredients of 
which were musk, salt, and " Tsang-eul-tsee." 

The writings of the early" Greeks contain very little 
reference to dental hygiene, and as far as caries is con- 
cerned their attention seems to have been confined to 


relieving pain and hygiene of the gums ; yet how near 
Aristotle came to the modern conception of the cause of 
caries may be judged from this sentence taken from his 
book on " Problems ": 

" Why do figs, when they are soft and sweet, produce 
damage to the teeth ? Perhaps because the viscous 
softness of the fig causes small particles to adhere to the 
gums and insinuate themselves into the dental inter- 
stices, where they very easily become the cause of putre- 
factive processes." 

The only allusion made by Celsus to dental prophy- 
laxis is that, " after rising, if it be not winter, the mouth 
should be rinsed with a quantity of fresh water." To 
be avoided in winter probably because of the teaching 
of Hippocrates, that " Cold is the enemy of the teeth." 

Pliny states that the ashes of the head of a hare are a 
useful dentifrice, and if spikenard be added it will lessen 
the bad smell of the mouth. He also recommends burnt 
eggshells as a good tooth-powder. 

Toothpicks of bone and metal seem to have been used 
commonly by the Romans. And it is stated by T. Wright* 
that Saxon women carried toothpicks of ivory in their 

Messalina, the wife of the Emperor Claudius, we are 
told, used a dentifrice composed of calcined stags horn, 
sal-ammoniac, and mastich of Chios. And several writers 
of this time mention that old (ammoniacal) urine was 
popularly used to preserve the teeth. 

Paul of /Egina. during the seventh century, gives the 
following rules for the preservation of the teeth : All 
tainted food to be avoided, and also all possibility of 
indigestion and frequent vomitings ; the use of very 
hard or glutinous food, or of such as may easily leave a 
residuum between the teeth — for example, dried figs — 
and likewise very cold food and such as sets the teeth on 
edge should also be avoided. 

He advises, too, that hard things should never be 

* " The Celt, the Roman, and the Saxon " (London, 1852). 

All to be 




broken with the teeth, and that the latter be carefully 
cleaned, especially after the last meal of the day. 

A representative of Arabian science, Avicenna, pointed 
out (about a.d. 1000) that very hard powders should be 
avoided, as these were likely to damage the teeth, and 
he recommends the use of burnt hartshorn. 

During the fifteenth century, Giovanni of Arcoli drew 
up ten canons of dental hygiene which represented all 
the accepted teaching on the subject up to that time. 
The following is a brief summary of each canon : 

i. Nothing must be eaten or done which would inter- 
fere with digestion : 

2. Vomiting. 

3. Sweet and sticky food. 

4. Hard substances. 

5. Food which sets the teeth on edge. 

6. Food too hot or cold. 

7. Leeks. 

8. Teeth to be cleaned with a piece of stick after every 

9. The mouth to be washed out afterwards with an 
aromatic decoction. 

10. A dentifrice to be used last thing at night or early 
in the morning. 

It is with considerable surprise that one learns that 
so " advanced " a code of oral hygiene was advocated, 
and we ma}' presume practised, over four hundred years 
ago, and to the significance of this fact and to the 
inferences to be drawn therefrom we shall have occasion 
to refer later on. 

A century later (1580) we find Foreest of Leyden 
condemning the consumption of sweetmeats as harmful 
to the teeth. 

Passing on to the seventeenth century, a somewhat 
different line of preventive treatment is advocated by 
Riviere (1589-1655), who advised that the teeth should 
be cleaned with a small stick immersed in a mixture of 
" spiritus sulphuris aut vitrioli et mel rosatum," or, 


if the teeth were very dirty, to use the acid undiluted. 
Unfortunately, no records are given of the results 
obtained by this somewhat heroic treatment. 

Anton Nuck, a Dutch surgeon of the end of the seven- 
teenth century, gives a formula for a tooth-powder much 
used in his time. The ingredients were powdered cuttle- 
fish, coral-powder, cream of tartar, Armenian bole, and 
powder of red roses. 

During the next century we have Junker, Professor of 
Medicine at the University of Halle, recommending sage 
and also common salt to be rubbed on the teeth to 
preserve them from caries. 

From Pierre Fauchard's book, " Le Chirurgien Den- 
tiste," published in 1728, we learn that tooth-brushes 
made of horsehair were in use at that time. He himself, 
however, condemns their use, and advises that the teeth 
should be cleaned with a fine sponge and tepid water to 
which has been added a fourth part of aqua vitae. 
Instead of the sponge, the root of the marsh-mallow or 
lucern might be used. He also gives lengthy and com- 
plicated prescriptions for mouth-washes, the chief in- 
gredients of which seem to have been aromatics, alcohol, 
gums, and sweetening agents. The same author makes 
the following very decided statement : " Little or no 
care as to the cleanliness of the teeth is the cause of all the 
maladies that destroy them.'" 

Bunon m 1743, in an excellent work, pointed out the 
necessity of attention to cleanliness of the milk-teeth, 
and correctly stated the influence of disease of the latter 
over the permanent teeth. 

At the end of the eighteenth century two erroneous 
theories gained ground, and did much to negative the 
teaching of dental hygiene. The first of these, shared 
alike by Hunter and Bell, was that caries originated 
from within, and was influenced little, if at all, by 
external agencies. The second was that, in order to 
keep the teeth free from " tartar," it was desirable that 
coarse and gritty dentifrices should be used, and the 


resulting denudation of the enamel of the teeth did not 
at all matter, since it would be developed afresh (pre- 
sumably like nails or hair). 

This latter theory was, however, strenuously opposed 
by Thomas Berdmore, dentist to King George III., who 
performed experiments to show the destructive effect of 
these tooth-powders. 

Fox in 1814 stated that " the principal means of 
preserving the teeth from decay consists in paying such 
a degree of attention to them in early life, during the 
period of the second dentition, as to allow the per- 
manent teeth to acquire a proper regularity ; and when 
these circumstances have been observed, young persons 
should be urged to keep their teeth very clean, and the 
daily use of a tooth-brush, with water only, will in most 
cases be quite sufficient. In addition to cleanliness, the 
habitual use of all kinds of food at a moderate tempera- 
ture will most certainly prevent any disease from taking 
place, unless there be any radical defect in the teeth 

The methods adopted in America during the middle 
of the last century are given by Harris (1853) and 
Goddard (1854). The former, referring to experiments 
which had been done by Westcott ten years previously on 
the effect of various acids (including the acids produced 
by fermentation) on the teeth, states that he believes 
caries to be due more to acid oral secretions than to 
either acids introduced as condiments or tonics or 
formed by fermentation, and is of the opinion that if 
the functional operations of the bodv were properly 
performed, caries of the teeth would never occur. But 
he further states that it is necessary to artificially keep 
the teeth absolutely clean to avoid caries, and gives 
prescriptions for chalk dentifrices. 

Goddard lays great stress upon perfect cleanliness and 
the frequent use of the toothpick and floss silk, and 
he gives various formula for antacid, detergent, and 
aromatic dentifrices. 


Thus we are brought down to within measurable 
distance of the present time and it will be convenient 
now to briefly summarize the methods we have already 
considered as having been used for the prevention of 
caries. We thus find that from the very earliest times 
— from the dawning of a higher civilization — soft sweet 
foodstuffs were recognized as a factor in the causation 
of dental disease (Aristotle) ; that very hard substances 
were to be avoided ; that carbonate and phosphate of 
lime (as eggshells or burnt and powdered bones) were 
constantly prescribed as dentifrices ; that alkalies in the 
form of ammoniacal salts were also frequently used and 
prescribed ; that acids of all sorts were to be avoided ; 
that " aromatics " were usually combined with denti- 
frices ; that mechanical prophylaxis by means of tooth- 
picks and frayed-out wood was in vogue from earliest 

And all this before Pasteur had discovered the role of 
micro-organisms in the process of fermentation, or Lister 
had demonstrated the relationship of bacteria to disease 
and the method of eliminating them from diseased foci, 
or Miller had shown that caries of the teeth depends 
upon the formation of acids produced by the action of 
organisms on carbohydrate foodstuffs. 

After these epoch-making discoveries, surely it would 
be thought that enormous strides would have been made 
in the preventive treatment of this particular disease ; 
that the rationale of prophylaxis would have undergone 
a complete change ; and that the incidence of caries 
would have been materially lessened. But has this 
been so ? 

On all counts we are bound to answer in the negative. 
True, for some time after the discovery of antiseptics, 
such drugs were largely used in the mouth in order to 
endeavour to eliminate the bacterial factor ; but it was 
soon found that it was impossible to sterilize the oral 
cavity, or even to decrease appreciably the number of 
organisms present, for even an hour, without using drugs 


in such strength as could not be tolerated, on account 
of their disagreeable taste and deleterious effect on 
the oral mucous membrane. So that the routine use 
of antiseptics for this particular purpose has largely 
been given up. 

What, then, are the means employed at the present 
time for the prevention of dental caries ? 

Naturally, they are numerous, and it is impossible 
here to review them in detail ; but the principles gener- 
ally recognized may be gleaned from at least two widely 
accepted authorities. The British Dental Association, 
in its pamphlet on the preservation of the teeth (1905), 
advocates — 

1. The use of a small tooth-brush with stiff bristles, 
used after the last meal. 

2. The use of alkalies, such as soap, chalk, whiting, 
and also common salt. 

3. The use of hard food. 

Dr. Rose of Munich, like Giovanni of old, has drawn 
up a decalogue for the care of the teeth, in which he 
advocates — 

1. Education of children and guardians in oral hygiene. 

2. Mechanical cleansing of the teeth with a suitable 
brush or toothpick. 

3. Avoidance of soft sweet foods. 

4. Active mastication. 

5. Alkaline and antiseptic dentifrices and mouth- 

Can it be possibly claimed that these measures differ 
in any fundamental principle from those which have 
been in the main practised ever since decay of the teeth 
has been treated by civilized man ? 

Compare the teaching of the nineteenth and twentieth 
centuries with that of the fifteenth, and it will be seen 
to be almost identical, differing only in one respect — 
the advocacy of " active mastication." 

In view of the fact that the incidence of dental caries 
has not decreased, but increased, in geometrical ratio 


almost, during the last 500 years, and in view of the fact 
that a similar line of preventive treatment has been 
systematically carried out for the last five centuries, 
what inference are we entitled to draw ? 

A priori, it would seem obvious that the treatment 
was radically wrong ; that the judgment of time and 
experience alike condemned it, or at least some im- 
portant part of it ; and that such measures have proved 
futile to arrest the progress of what has become the most 
prevalent disease of civilized communities. 


Densham : Proceedings of the Royal Society of Medicine : 
Odontological Section, vol. ii., p. 71. 

Henderson : British Dental Journal, vol. xxix., pp. 350, 392, 


Harris : Principles and Practice of Dental Surgery, 1853. 

Guerini : History of Dentistry, 1909. 

Fox : Natural History and Diseases of the Human Teeth, 18 14. 

Goddard : Anatomy, Physiology, and Pathology, of the Human 
Teeth, 1854. 



A. Racial. 

It is now universally admitted that dental caries is to a 
great extent a disease accompanying civilization, and 
that its numerical incidence is largely proportionate to 
the state of civilization to which a particular race has 
attained. Nevertheless, it will be useful here to briefly 
recapitulate the evidence which has given rise to this 

Magitot, 1 examining the skulls in the Paris museums, 
found no caries of the teeth in the following races : 
Mexicans, Peruvians, Patagonians, aborigines of Aus- 
tralia, Madagascar, New Caledonia, the Malay Peninusla. 
or Java. 

The now classical research of J. R. Mummery 2 into 
this question shed considerable light on the subject. The 
results of his investigation into the prevalence of caries 
in existing primitive races may be classified as follows : 




Indians of N.W. American Coast 

Fiji Islanders 

Northern Hindoos 

Xorth American Indians 

Eastern Polynesians 

Southern Hindoos 


Sandwich Islanders 



Negroes (slaves) 


Percencage of 
Skulls showing 
Carious Teeth. 

i '4 


9 - 5 
1 1 '4 


Such statistics as these, although tabulated here in 
the apparent order of prevalence, cannot be accepted 
as representing exactly the true state of affairs, since the 
number of skulls of each race examined varied con- 
siderably, and was in no case very large ; neither is the 
proportion of sound to carious teeth given. Also, of 
course, the ages of the skulls in each race probably 
varied considerably. 

Again, some in each race may have been Paleolithic, 
some Neolithic, and some from quite recent times. 

Nevertheless, in spite of these fallacies, the tables 
may be taken, I think, as representing roughly the 
comparative prevalence of caries in the different races. 

Comparing now the incidence of caries in uncivilized 
races with that in civilized races of the present time, a 
vast difference is observed. The Physical Deterioration 
Committee reported in 1904 that " there is no doubt 
that the teeth of the people have become much worse 
of late years, and in many parts of the country may 
now be described as very bad/' There can be no doubt 
that these words do not err on the side of exaggeration, 
as the following statistics will prove 



of Persons 

Class of Person examined. 

of Persons 





English and Scotch 



British Dental As- 

school boys and girls 

sociation 3 

Residents of Baden 1 


Rose 3 

and Hamburg I 

\ 96*40 J 

Halifax children 



M.O.H. for Halifax 3 

Leith school-children 



Robertson 4 

Kettering children . . 

5- 7-24 


Layton 5 

Birmingham school- 





Cambridge Dental 





School - children of 




Northern Germany 

Dental As:--ocia- 

Per Cent. 






These figures show a quite remarkable uniformity. 

The British Dental Association's report is, I believe, 
less recent than the others ; so that this would tend to 
show that even in quite recent years the number of 
persons affected with caries is increasing. 

It is also of interest and some importance to compare 
the increase in the prevalence of caries which has occurred 
in individual races. 

Mummery, investigating the number of Ancient British 
and Anglo-Saxon skulls showing carious teeth, gives the 
following figures : 

British skulls of the Stone Age showed carious teeth in 
British skulls of the Bronze Age showed carious teeth in 
Romano-British skulls showed carious teeth in . . 
Anglo-Saxon skulls showed carious teeth in 

Wright 8 examined the Driffield Collection of Skulls 
from the barrows of the East Riding of Yorkshire. 
They belonged to the Bronze and Early Iron Ages. 
The percentage of actual caries was only 1*5. Wright, 
in the communication referred to, attributed " alveolar 
abscesses to caries," and this, of course, made the per- 
centage much higher ; but, from my own experience in 
the examination of skulls and teeth of uncivilized races, 
I think that such an inference was probably erroneous, 
since alveolar abscesses result in such races most com 
monly through an opening up of the pulp cavity due to 
excessive attrition, without the slightest trace of caries. 

An examination of 562 skulls from long barrows gave 
8 per cent, of caries, and 47 skulls from round barrows 
showed 21 per cent. 

In an examination of 260 Maori skulls — all from an 
uncivilized age — I found carious teeth present in only 
two skulls, or 076 per cent. 

Taking the average of Mummery's and my own 
investigations, the incidence of caries in the Maori is 
1*2 per cent, in a total of 326 skulls. This is lower even 
than the Esquimaux, and shows the Maori to have been 


the most immune race to caries, for which statistics are 

Comparing these figures with those applicable to the 
present time, we find that the descendants of the Britons 
and Anglo-Saxons are afflicted with dental caries to the 
extent of 86 per cent, to 98 per cent. ; and after examin- 
ing fifty Maori school-children living under European 
conditions entirely, I found that 95 per cent, of them 
had decayed teeth. 

It will be of interest now to compare the percentage 
of carious teeth found in uncivilized races and the higher 
civilized races of to-day. 

Patrick 9 has examined all the " prehistoric crania to 
be found in the various museums in America." The 
results are as follows : 


Asiatics (including Malays, Chinese, 

Japanese, Armenians, Hindoos, and 

Egyptians and Africans 
Polynesians and Australians 
Central Americans 

North Americans (including Esquimaux) 
South Americans (including Tierra del 

Fuegians and Guanches) .. .. 6,719 5*804 

Europeans (including " a few modern I 

soldiers ") . . . . . . . . 3.422 



of Teeth 

of Carious 













Comparing these low percentages of carious teeth with 
those obtaining at present, we find that Ottofy, 10 after 
an examination of 14,644 teeth of American school- 
children, reported that 30 per cent, were carious. 
Cunningham, 7 reporting on the work of the Cambridge 
Dental Clinic, gives statistics which show that 523 per 
cent, of the teeth of the children examined (1,403) were 


In an examination of two schools of Maori children 
living under civilized conditions, I found that 15-6 per 
cent, of the teeth were carious. 

Very few statistics of this nature are available, and 
it is a matter for regret that, when examinations are 
made, the number of sound teeth and carious teeth 
in each mouth are not tabulated more frequently ; for, 
after all, this is by far the most important and serious 
aspect of the present prevalence of this disease. 

If the incidence of caries per head of the population 
were 100 per cent., but if only 5 per cent, of the total 
number of teeth were affected, there would be but little 
work for the dental profession and no occasion for the 
present argument. 

Summing up the results of these investigations, we 

1. That the number of persons affected with dental 
caries who live under uncivilized or "natural " conditions 
is comparativeh' small, varying from 1 to 20- 8 per cent., 
whilst in civilized modern races the percentage is as high 
as 98 per cent., the increase being at least 77-4 per cent. 

2. That the number of teeth affected with caries in 
each individual is far less in those leading natural lives 
than in those leading artificial or highly civilized lives, 
in the former varying from 2 per cent, to 7 per cent., 
whilst in the latter it has become as high as from 15 per 
cent, to 52 per cent., showing a maximum increase of 
45 per cent. 

3. That in the British race, which has been subject to 
the influence of civilization for nearly 2,000 years, the 
increase in the percentage of caries is about 79 per cent, 
(calculated from the averages of the statistics given 
above) This corresponds closely to the difference in 
percentage given above in No. 1. 

4. That in the Maori race, which has been subject to the 
influences of civilization for only seventy or eighty years 
at the verv most, but has onlv become " civilized " in 


habits quite recently, the increase is one of 93 per cent. 
(But against this apparently high figure has to be set 
the fact that the incidence of caries in each mouth is 
comparatively low.) 

Reviewing now all the above investigations, we are 
clearly justified in our original statement that there is 
a distinct relationship between the incidence of caries 
and the state of civilization. An interesting example 
of this is found in the fact that the prevalence of dental 
caries apparently fell in England after the invasion by 
the Anglo-Saxons — a race less civilized than the Roman- 
ized Britons whom they displaced. 

Civilization though, per se, cannot be the cause of so 
much difference in the incidence of caries. For instance, 
the Maori was undoubtedly a more " civilized " and a 
higher type of savage than the Zulu, the Esquimaux 
than the Bushmen, and the North American Indians 
than the Australian aborigines ; yet in each of these 
cases the race of higher type showed the least incidence 
of caries. 

It must be, then, some particular, though not always 
essential, accompaniment of civilization which is re- 
sponsible for the increase. Naturally, one would expect 
that factor of civilization which particularly affected the 
function of the teeth to be responsible, and this un- 
doubtedly is so to a very large extent. The function 
of the teeth is primarily to masticate food, and there 
can be no doubt that in those races in which this func- 
tion is most perfectly carried nut, and in which the 
teeth have the most natural work to do, dental caries 
is correspondingly rare. In fact, it would be more 
correct to say that the numerical incidence is largely 
proportionate to the state of " civilized " diet to which 
a particular race has attained. The physical, chemical, 
anatomical, and physiological effects of this dietetic 
evolution on the teeth will be considered in detail 


B. Sexual. 

The opinion seems to be unanimous that females are 
slightly more liable to caries than males. Statistics 
vary on the point. Magitot gives the difference as 
25 per cent, in favour of males. Rose gives the per- 
centage of caries in boys as 26, and in girls 26-2. Greve 11 
states that 3 per cent, more girls than boys are affected 
with caries. 

C. Age. 

Since statistics bearing upon the incidence of dental 
caries are almost entirely based upon the examination 
of school-children, it is difficult to give any precise data 
as to the percentage of incidence in later life, but in 
general terms it may be stated that caries is essentially 
a disease of adolescence. It is a matter of common 
observation that the progress of the disease in any par- 
ticular mouth is much slower, and even may be altogether 
arrested, after the patient has attained to adult life. 
Or, expressed otherwise, if a tooth remains free from 
decay for some years — say eight to ten — after eruption, 
there is a strong probability that it will remain immune 
for at least a prolonged period. This is an important 
fact, and will be referred to later. 

The accompanying diagram (Fig. 1), drawn up by 
Mr. F. W. Richards, illustrates graphically the rapid 
increase in incidence of caries between the ages of six 
and thirteen. It illustrates not only the fact that the 
number of carious teeth increases, but also — more serious 
— the much increased extent of the disease in each tooth. 

Cunningham's figures show a similar increase, but the 
incidence of caries is much higher throughout. Thus, 
at three years old the percentage of children having 
carious teeth is 84. This increases steadily up to the 
fourteenth year, when the number reaches nearly 100 
per cent. 



Greve's statistics, however, do not agree with the fore- 
going. He gives 93-3 per cent, at six years, 96-5 per 


but not 
all filled 

Fig. 1. — Diagram graphically representing the Relative 
Liability to Caries according to Age. 

[By permission of the "British Dental Journal.") 

cent, at ten, and 94/5 per cent, at fifteen. Evidently, 
caries of the deciduous teeth is very prevalent amongst 
German children. 

D. Susceptibility of Different Teeth. 

The report of the work of the dental surgeons of the 
United States Army for the years 1901-1903 afford the 
most valuable information on this point, since over 
70,000 teeth were treated by fillings and extractions. 
It is not proposed to give here the percentages of each 
tooth treated. It will be sufficient for our purpose to 
give the more important groups : 



Average Percentage 
of Each Carious. 

First permanent molars . . 
Second permanent molars 
Upper central incisors 



Third molars 


Upper canines 


Lower incisors 


Lower canines 


Hence it is obvious that certain teeth are, by reason 
either of their position or function, far more susceptible 
than others, the first molars being more than twelve 
times more susceptible than the lower canines, for 
instance, and the upper incisors five times as susceptible 
as the corresponding lower teeth. 

Another important fact borne out by this report is the 
increased susceptibility of upper teeth. Forty-three thou- 
sand upper teeth were carious, but only 26,000 lower, 
or nearly twice as many upper as lower teeth. 

This confirms Hitchcock's figures, 12 compiled from 
20,000 cases of fillings and extractions. He found 
13,136 upper teeth and 6,864 lower teeth carious — 
again a proportion of nearly two to one. 

Magitot, however, gives the proportion as three to 
two in an analvsis of 10,000 cases. 


1 Magitot : Marshall's Operative Dentistry, p. 122. 

2 Mummery, J. R. : Transactions of the Odontological Society, 
vol. ii., New Series. 

3 Rose and British Dental Association Report, quoted by 
Smale and Colyer in " Diseases and Injuries of the Teeth," p. 242. 

4 Robertson : British Dental Journal, 1909, p. 655. 

5 Layton : British Dental Journal, 1908, p. 865. 

6 Richards : British Dental Journal, 1909, p. 751. 

7 Cunningham : British Dental Journal, 1908, p. 872. 

8 Wright, W. : British Dental journal, 1903, p. 57. 

9 Patrick: Marshall's Operative Dentistry, p. 121. 

10 Ottofy : Marshall's Operative Dentistry. 

11 Greve : Cor. Blatt. fur Zahn., July, 1899. 

12 Hitchcock : Wedl's Pathology of the Teeth. 




It would serve no useful purpose here to review in detail 
all the theories which have been at various times put 
forward to account for the phenomena of dental caries. 
It will be sufficient to briefly mention the more important 

Hippocrates advanced the theory that caries, in com- 
mon with all other diseases, was due to a disturbance of 
the four principal humours of the body, and this theory 
was not extinct even as late as 1757. 

The belief that the disease was a vital process, was 
in reality a form of inflammation similar to caries of 
bone, has been held by a large number of celebrated 
authorities from Galen down to Hunter and Fox, and 
Abbott in 1879 strongly supported the theory. 

In the Middle Ages the worm theory of caries was much 
in vogue, and quacks (and also physicians) used various 
fumigations for expelling the " worms " — a method still 
practised by quacks in some parts of Italy. More 
modern theories are — 

1. The Electrical Theory, enunciated by Bridgeman, 
in which each tooth is supposed to act as a small galvanic 
battery, setting up currents which hydrolyze any stag- 
nating food debris, thus setting free acids which produce 

2. The Chemical Theory. — That acids were destructive 
to the teeth has been recognized from quite early times, 
and Westcott in 1843 showed that acids, whether organic, 
inorganic, or produced by " fermentation," might dis- 



solve the enamel, and so cause caries. Harris (1853) 
stated his belief that caries was caused by acidity of the 
oral secretions, and Sir J. Tomes (1873) ascribed the 
cause of decay to the process of fermentation and acid 

3. The Septic Theory, advanced by Milles and Under- 
wood, in which caries is said to be due to the action of 
acids and the action of germs, the germs secreting the 
acid from the protoplasm of the organic fibrils upon 
which they live. 

4. It remained, however, for Miller (1885) to advance 
what is now known as the Chemico-Parasitic Theory, 
which alone satisfactorily accounts for all the phenomena 
of caries of the teeth. This theory is most universally 
accepted at the present time, and it is accepted as the 
pathological basis of the author's investigations to be 
hereafter described. The important points in the 
chemico-parasitic theory are — 

(1) That the organisms of the mouth, by the secretion 
of an enzyme (or by their own metabolism), so act upon 
carbohydrate food material as to form acids by a process 
of fermentation. The chief acid formed is lactic, but 
butyric, acetic, formic, succinic and other acids may 
also be formed. 

(2) Carbohydrate food material lodging between or 
on the teeth is the source of acid, which attacks the 
lime salts of the enamel, dissolving the interprismatic 
cement substance. Thus by the action of the acid and 
by the force of mastication the enamel is destroyed or 
weakened, and removed mechanically. 

(3) The action of the micro-organisms of the mouth 
upon protein material is to form an excess of alkaline 
substances which have no action upon the enamel other 
than a beneficial one. 

(4) The enamel being penetrated, the solution of the 
lime salts of the dentine is brought about in the same 
manner, the organisms penetrating along the dentinal 


(5) The further stages of caries of dentine is brought 
about by another set of organisms which secrete a pro- 
teolytic enzyme. This dissolves the collagen of the 
dentine matrix, thus forming a cavity. 

Goadby* has classified the organisms concerned in the 
production of caries as follows : 

Acid-forming Bacteria. 

1. Streptococcus brevis 

2 . B. necvodentalis 

3. Staphylococcus albus 

1 . Streptococcus brevis 

2. Sarcina lutea 

3. Sarcina alba (Eisenberg) 

4. Staphylococcus albus 

5 . Sarcina aurantica 

6. Staphylococcus aureus 

Deep layers of carious dentine. 

Superficial layers of carious 

Bacteria which liquefy Dentine [Decalcified.) 
None isolated . . . . Deep layers of carious dentine. 

1. B. mesentericus ruber 

2. B. mesentericus vulgatus 

3. B. mesentericus fuscus 

4. B.fuvvus 

5. B. gingiva pyogenes 

6. B. fluorescens liquefaciens 


7. B. subtilis 

Superficial layers of carious 

The following equations express briefly the phenom- 
ena of lactic acid fermentation as it takes place in the 
mouth : 

Monosaccharides : 
C 6 H 12 O fi 


2(C 3 H 6 3 ), 

Lactic acid. 

Disaccharides : 

C12H22O11+ H 2 =C 6 H 12 6 + C 6 H 12 6 . 

Cane-sugar. Dextrose. La;vulose. 

C 6 H 12 6 

2C 3 H 6 3 . 

Lactic acid. 

Mycology of the Mouth." 


Polysaccharides : 

(C 6 H 10 5 ) n +H 2 0=C 6 H 1 o0 5 +C 12 H 22 11 . 

Starch. Dextrin. Maltose. 

C 12 H 22 O n +H 2 0=2C 6 H 12 6 . 
2(C 6 H 12 6 )= 4 (C 3 H 6 3 ). 

Lactic acid. 

2(C 3 H 6 3 ) =C 4 H 8 2 + C0 2 + 2H0. 

Butyric acid. 

This shows that monosaccharides are directly fer- 
mentable, and that disaccharides require to be first 
inverted to monosaccharides by an enzyme formed by 
certain of the mouth organisms before lactic acid is 
produced. Starches require a double inversion, the first 
stage brought about either by ptyalin or organisms, 
before fermentation to an acid can occur ; but in all 
cases it is seen that lactic acid is the end product, unless, 
as occasionally happens, this lactic acid is again split 
by the action of organisms to yield butyric acid. 

Perhaps the most convincing proof of the validity of 
this theory is the fact that in accordance with it caries 
can be artificially produced in the laboratory so as to 
resemble in its microscopical features all the phenomena 
of natural caries. For this purpose it is only necessary 
to take a portion of such food as would constitute an 
ordinary meal (carbohydrates preponderating), inocu- 
late it with saliva, place a tooth whole or in section in 
the mixture, and incubate. In twenty-four hours the 
mixture will be found to be markedly acid. The acid 
continues to increase daily, and may under these cir- 
cumstances become so strong as to destroy the acid- 
forming organisms. To avoid this, a little sodium 
hydrate or carbonate should be occasionally added. In 
about fifty days the teeth may be removed and examined, 
with the result as above stated. 

It is contended by Leon Williams and Black that the 
essential feature in the pathology of caries is the presence 
of bacterial plaques upon the surface of the teeth, and 


that the lactic acid is secreted as such by the organisms 
themselves. Since this has a bearing upon the preven- 
tive treatment of caries, it is necessary to consider the 
importance of this claim. 

i. The presence of plaques is undoubted, but they 
occur on all surfaces of teeth, and not solely on the 
mesial and distal surfaces, which are most liable to 
attacks of caries. Thev occur on the teeth of immune 

Fig. 2. — Bacterial Film on the Surface of Arrested 
Caries of Dentine. 

people apparently as frequently as upon the teeth of 
susceptible persons. They are found upon animals' 
teeth ; they are found upon the inner surface of secondary 
enamel decay.* A bacterial film may be demonstrated, 
too, upon the surface of teeth in which the process of 
caries has been naturally arrested and the dentine become 
quite hard, where, if anywhere, one would expect an 
acid-forming film of bacteria to be absent (see Fig. 2). 

* Miller, Dental Cosmos, 1902, p. 437. 


2. If the film of organisms is the essential origin of 
the acid, it would tend to constantly remove itself by 
dissolving its base of attachment. 

3. The film of organisms cannot produce acid from 
Nasmyith's membrane nor from the oral secretions. 
They must have a supply of carbohydrate medium for 
the purpose, and this must remain in apposition for a 
sufficient length of time for enough acid to be 
" secreted." 

4. The saliva, which almost immediately permeates 
all food upon mastication, contains millions upon millions 
of organisms capable of transforming carbohydrates into 
acids. Why is it then necessary to look to any par- 
ticular colonies for the formation of that acid ? 

We therefore come to the conclusion (1) that bacterial 
plaques upon the teeth are not an essential factor in the 
causation of caries ; (2) that the lodgment and infection 
of carbohydrate material is the essential factor, and that 
those circumstances which favour the formation of bac- 
terial plaques upon the teeth also favour the lodgment 
of carbohydrates, and so the occurrence of the two 
usually coincides. 

Therefore it is evident that the two essential attack- 
ing forces in this disease are, (1) the acid-forming organ- 
isms of the mouth, (2) the presence of fermentable 
carbohydrates — the first active, the second passive. 

The inception and progress of the disease are, how- 
ever, by no means so simple as would appear from the 
above statements and equations. The phenomena are 
profoundly modified by a large variety of factors, such 
as the character and number of organisms present, the 
variety and amount of carbohydrate material available for 
acid production, the amount, alkalinity, and diastatic 
action of the saliva, the resistance of the enamel surface, 
the shape and development of the jaws and the dis- 
position of the teeth. And since these conditions vary 
in different individuals, it is evident that the possible 


permutations and combinations of the various factors 
are very numerous and complex. In fact, dental caries 
is similar to many other diseases. It is not the " effect " 
of any single " cause," but it is the resultant of several 
forces — it may be few or many, and not always similar — 
acting in one general direction, and which happen for a 
longer or shorter period to be coincident. 

Dental Caries as a Source of Oral Sepsis. 

During the first stage of dental caries, when the 
enamel only is being dissolved by means of lactic acid, 
it can scarcely be said that sepsis, in the ordinary sense 
of the word, is present ; but as soon as the dentine 
becomes involved in the morbid process there can be 
no doubt that sepsis is present — sepsis, but not sup- 

The proteids of the fibrils and dentinal matrix are 
being metabolized largely by pyogenic organisms giving 
rise to poisonous end-products — gases such as carbon 
dioxide, sulphuretted hydrogen, indol and skatol. and 
liquid toxins, albumoses. etc.. all of which must be 
swallowed by the patient. Before the pulp is actuallv 
exposed, it is frequently infected by organisms passing 
down the dentinal tubules, and suppuration, either 
localized or general, occurs in the pulp without there 
being any external evidence of its presence ; the products 
of this suppuration must, of course, be wholly absorbed 
by the lymph and blood streams. A stage further, 
and the pulp is exposed, and sooner or later becomes 
gangrenous — septic in the highest sense of the word — 
and again all the gangrenous products are swallowed 
by the patient. 

In the final stages the periodontal tissues become 
infected through the apical foramen, suppuration occurs, 

* The term "sepsis" is now* used so frequently as being 
synonymous with suppuration that we lose sight of its real 
meaning [<riprta = l make putrid), and the destruction of dentine 
is really a putrid process. 


and an alveolar abscess develops, which, if not treated, 
becomes chronic and is a persistent source of oral sepsis, 
the septic products in this case being partly absorbed by 
the lymphatics, and partly swallowed. It is therefore 
quite clear that the most rational method of eliminating 
these various sources of sepsis and septic absorption is 
to take means to prevent the commencement of the 
carious process at the enamel surface. 

Other Sources of Oral Sepsis. 

Any chronic inflammatory lesion within the mouth is 
to be regarded as a source of oral sepsis ; in many of 
these conditions pus is present from the commencement, 
and in many more, suppuration is sooner or later estab- 

Such conditions are the various forms of stomatitis, 
glossitis, and gingivitis ; but the most common of all is 
that known as " pyorrhoea alveolaris," * and it may not 
be out of place to refer briefly here to the pathology 
of this latter lesion. It is essentially a suppurative 
process occurring in the joint around a tooth between it 
and the jawbone ; it may be localized or general, but 
usually is found associated with groups of several con- 
tiguous teeth. 

As a general rule, the resistance of the gingival tissues 
is lowered either by some general constitutional disorder 
(i.e., chronic nephritis, diabetes, syphilis) or by the local 
accumulation of salivary calculus around the necks of 
the teeth. The " gums " become slightly thickened, 
congested, and dusky in appearance. Infection by oral 
micro-organisms occurs, and this affects chiefly the 
dental surface of the gingival fold of mucous membrane, 
giving rise to ulceration ; soon the infection spreads 
downwards to the periodontal ligament, the upper part 
of which is destroyed, leaving a small cavity or " pocket " 

* A bad term ; various others have been suggested. The 
author believes suppurative dental arthritis is pathologically 


which nils up with pus. The bone of the socket, being 
thus opened to infection, is next attacked by a rarefying 
osteitis : thus, inflammation and destruction of the 
periodontal ligament, and inflammation and destruction 
of the alveolar bone continue synchronously, until the 
joint is totally disorganized and the tooth is so loose that 
it is either accidentally dislocated or is removed sur- 
gically. The duration of the disease may vary from a 
few months to several years, but during the whole of 
this time pus is continually being formed and discharged 
into the mouth. When such a '" suppurative arthritis " 
is general, it constitutes a very potent but frequently 
overlooked, because painless, source of " oral sepsis." 
and almost invariably originates grave secondary sys- 
temic disorders due to chronic toxaemia and sapraemia. 




Effect of Soft Food on the Development of the Jaws and 
Resistance of the Teeth. 

Ceteris paribus, it is admitted that irregularities in the 
position of the teeth in the direction of " crowding " 
lead to an increase in the incidence of caries. This would 
seem to be obvious from the increased facilities afforded 
for the lodgment of fermentable foodstuffs., and from the 
increased difficulty of the teeth being cleaned either 
naturally or artificially. 'Yet this is by no means 
universally true, as we shall have occasion to point out 
later. Some mouths with crowded and irregular teeth 
are comparatively free from caries, and. conversely. 
many dentures perfectly symmetrical are often rapidly 
destroyed by decay.) 

It therefore becomes necessary to consider briefly the 
cause and prevention of crowding of the teeth, in order 
to understand how this cause of the lowered resistance 
of teeth to caries may be removed. Expressed in a 
popular way, when the teeth are in marked malocclu- 
sion, it is said that " there is not room for them in the 
jaw," or. put otherwise, that the jaws are too small for 
the teeth ; and this in the majority of cases is a perfectly 
accurate statement. 

In some instances, undoubtedly, the condition arises 
through heredity pure and simple, a child inheriting the 
large teeth of one parent with the small jaws and features 




of the other ; but in the larger percentage of cases there 
is no reason to suspect this cause, and the jaws are too 
small for the teeth because they have not developed to 
their full dimensions, and they have not developed 
because they have not been used to their full phvsio- 
logical extent. 

It may be stated as a physiological axiom, that the 
bones of those individuals who possess the strongest 
muscles are much better developed than those of persons 

Fig. 3. — Transverse Section of Jaw in Molar Region 

showing interarticular inclined planes. 

By permission of Professor Cryer.) 

with weak muscles. The full development of the bones 
is dependent upon the musculature, and the latter, of 
course, upon exercise of function and the amount of 
resistance to be overcome. 

Now, the exercise which the muscles attached to the 
mandible are called upon to perform is chiefly that of 
mastication of food. If the food be semi-liquid and 
soft, verv little muscular effort will be called forth, the 


muscles will not develop, and the mandible to which 
they are attached will likewise remain undeveloped ; 
and. on the other hand, a harder diet will stimulate 
greater muscular and osseous development. Such 
development, amongst other ways, may be manifested 
by an increased length and width of the mandible. 

There is another aggregation of muscles, through the 
tongue, which is. or should be. largely used in the act 
of mastication ; and. as is well known, the tongue has a 
distinct influence over the lower jaw in expanding it 
outwards and forwards. 

If the mandible fails to develop in the manner indi- 
cated, and it remains shorter and narrower than it 
should be. the upper jaw is also affected, and a condi- 
tion of A-shaped arches and palate supervenes, with, as 
a rule, considerable crowding of the teeth. Reference 
to Fig. 3 will show that the lower teeth articulate with 
the upper teeth by means of inclined planes from within 
outwards, and that any outward movement of the lower 
teeth is bound to be followed by a corresponding move- 
ment in the upper teeth ; and if this does not take place, 
neither can the upper teeth move outwards. 

In support of this is the fact that it is the lower tooth 
always which erupts first, and to a large extent thus 
determines the position of the corresponding upper tooth. 

Comparatively few muscles are attached to the upper 
jaw. It is not movable, and its stimulus to growth and 
development must come largely from the impact and 
grinding of the lower teeth against the upper in the act 
of mastication. 

Of recent vears much has been written to show that 
the diet of modern civilized races is becoming softer 
and " more pappy." It would seem to be one of the 
accompaniments, the refinements, the luxuries, which 
have always attended that phase of social evolution 
known as " higher civilization." 

There seems to be inbred in all animals and races of 
mankind an instinct or almost unconscious tendency to 


procure food in the most nutritious and assimilable form. 
This, of course, originally was but fitting and right, and 
no doubt has played a most important part in evolution 
and the survival of the fittest. But, unfortunately, now 
that civilized man has evolved to a position where the 
obedience to such natural instincts seems to be no longer 
necessary for his survival, he still retains most strongly 
this craving for the maximum of nourishment in the 
minimum of space, with the result that, in order to 
satisfy the modern taste in diet, all that is fibrous, all 
that is " coarse," or apparently " inert," is most care- 
fully eliminated from all articles of food — firstly by the 
grower, by a process of arbitrary selection, then by an 
elaborate system of mills and refineries, and finally by 
the cook. Anything that can by any possibility be 
termed " tough " is anathema. 

In this manner and by such means are the teeth and 
jaws robbed of their normal physiological functions. A 
large part of the energy which is developed by the 
enormous machinery in modern mills and refineries 
represents work which should be being done by human 
muscles of mastication. 

The effect is obvious and irresistible. The muscles 
and the bones dependent on them fail to develop to 
their normal extent. 

The jaws therefore become too small for the teeth 
when erupted (and also probably before eruption). The 
teeth take up irregular and crowded positions, and thus 
their resistance to caries is very considerably lessened 
because of the ease with which foodstuffs lodge between 
them, and the increased difficulty of its removal either 
by natural or artificial means before it has undergone 

The lesson is obvious. In order to eliminate this 
factor in the causation of dental caries, the desire for 
the superlatively nutritive must be combated. 

One might as well expect the bones of the arm to 
develop to their full and normal extent by keeping the 


arm constantly in a sling from infancy, as expect the 
teeth and jaws to develop normally when their natural 
function is kept in abeyance, as it is by the prevalent 
and habitual consumption of pretriturated and predi- 
gested food. 

G. V. Black* has shown by means of the gnatho- 
dynamometer that the force of the bite or strength of 
the masticatory muscles may in favourable individuals 
be equal to 300 pounds, but that in people whose diet is 
habitually a soft one the maximum pressure capable of 
being exerted may be as low as 50 pounds ; and. as 
Black points out. once this habit has been established, 
it tends to increase, since the periodontal membranes 
become tender from lack of pressure, and any increase 
of force is resented by the teeth. 

Children especially should be encouraged to eat hard 
and more fibrous foods, and not to be afraid of anything 
either tough or hard. In my opinion, this latter heresy. 
promulgated alike by dentists and laity, is responsible 
for a large percentage of the incidence of caries. Chil- 
dren (and adults) are carefully warned not to crack nuts 
with their teeth, not to bite anything hard, lest they 
should damage the enamel. The consequence of this is 
that the majority of people are of the opinion that the 
" enamel " is little more than a veneer, a delicate tissue, 
and easily destroyed, and great care is taken (as they 
think) to preserve it. Enamel, it cannot be too widely 
known and appreciated, is the hardest organized tissue 
in Nature. Its thickness over the cusp of teeth is 
quite considerable, and such as under ordinary circum- 
stances would take very many years to wear through. 
Its average thickness is 2-3 millimetres, and Black 
has shown that the enamel of ordinary teeth will resist 
without fracture a force of 350 pounds suddenly applied 
(hard vulcanized rubber being against the enamel). 

It is between the ages of six and twelve that the jaws 
as a rule fail to develop to their normal size — sufficient 

* " Operative Dentistry." 


to accommodate the teeth. It is therefore during this 
period that particular attention should be paid to the 
masticatory function. 

Such an increase in the inert matter in a dietary as 
has been advocated will probably be of benefit, too, in 
preserving the " tone " of the intestines, since a con- 
siderable proportion of the habitual constipation so 
common at the present time is undoubtedly due to an 
atonic condition of the bowels brought about by having 
deficient mass to transmit. 

This question, though, cannot be closed without say- 
ing a word on the other side, for it is quite possible to 
carry the doctrine of a fibrous dietary to an unwise 

There is no doubt but that the craving in civilized 
man to eliminate the inert from his food is to some 
extent a natural and physiological instinct, and as such 
should not be interfered with. 

The life of modern communities is becoming compara- 
tively sedentary, with the advent of compulsory educa- 
tion, tramcars, 'busses, and motor-cars. At the same 
time this is essentially an age of " hustling " and mental 
excitement, and it is entirely questionable whether under 
such conditions the stomach and intestines are capable 
of adequately dealing with food in a very bulky condi- 
tion. So that at least two precautions should be taken 
when advising a patient to adopt a coarser diet — firstly, 
to see that the change is not made suddenly, but is pro- 
perly graded ; and, secondly, that the patient's habit of 
life as regards exercise, etc., can be made to accord 
with the dietary. If these be not observed, the result 
will probably be gastralgia and a return to the pap 

Coarse and fibrous food does, of course, in time wear 
away the enamel from the occlusal surfaces of the teeth, 
and sometimes down to the pulp-chamber, though, if 
the process has been very slow, this cavity is usually 
filled in by secondary dentine. Sometimes this repara- 


tive function does not take place, and the result is an 
exposure of the pulp, with its subsequent necrosis and 
the formation of an alveolar abscess. This is not an 
uncommon occurrence in uncivilized races, and an 
example is shown in the accompanying photograph 
(Fig. 4). Uncivilized people, although comparatively 

Fig, 4. — Abscess Cavities caused through Excessive 

free from caries, must have experienced and do suffer 
considerable " toothache." Occasionally cases of marked 
attrition are observed in " civilized " persons at the 
present time ; and when this is so. the teeth are almost 
invariably remarkably free from caries. 


Other Factors influencing the Disposition of the Teeth. 
A. Habits. 

The acquisition of certain habits in early childhood 
which tend to constrict the jaws also tend, of course, to 
diminish the resistance of the teeth to caries. Such 
habits are usually " sucking habits," such as " dummy " 
or " comforter " sucking, finger-sucking and lip-sucking. 
These all tend to bring abnormal muscular force to bear 
upon the jaws at improper situations, and so help to 
distort them and cause crowding of the teeth. 

The finger- sue king may as a rule be prevented by 
tact and firmness (and perhaps a little mustard) ; the 
" dummy " sucking, however, is a more difficult ques- 
tion. By " dummy." I mean not only the bottleless 
rubber teat, but also the teats generally used in the 
artificial feeding of infants. 

There are some things to be said in favour of the 
rubber teat : 

1. They are frequently necessary when natural feeding 
is impossible. 

2. They insure nasal breathing, and in this tend to 
induce a good habit and one having a beneficial effect 
upon the shape of the jaws, and must therefore tend to 
prevent the formation of adenoids. 

3. The " bottleless " teat often insures a quiet, restful 
infant — a physiological condition much more conducive 
to normal growth and development than a restless, 
crying baby. 

It has been urged, too, as an argument in favour of 
the dummy, that since its use is restricted to the first 
two years of life at most, and since narrowing of the 
arch rarely appears before the sixth or seventh year, 
the two cannot possibly be connected as cause and 
effect. An inquiry into the facts of the case will there- 
fore be beneficial. 

The shape of the ordinary teat or dummy is, of course. 


quite wrong. It does not resemble the nipple of a 
mother's breast in the least, but its chief and most 
serious defect lies in its abnormal length. The " bulb " 
of the dumrrr passes right back to the posterior third 
of the tongue and the soft palate."" The effect of this 
may be gauged in an adult by sucking the thumb placed 
as far in the mouth as possible (the shape of the thumb 
and the length of it correspond proportionately, for the 
adult, quite closely to that of the dummy for the infant). 
The thumb is gripped by the tongue and the muscles of 


/tetito G/ossi/s. 

s/?t/sc/es $■ 

Fig. 5. — Diagrammatic Representation of Oblique Section 
through Posterior Part of Mouth andJOro-Pharynx, 
the Left Side being more Anterior than the Right. 

The arrows indicate the direction of contraction during 
" sucking." 

b, space ~entirelyJobliterated 

a, Space of negative pressure 
during sucking. 

the soft palate and anterior pillars of the fauces — that 
is to say, by the palato-glossus, superior constrictor of 
pharynx, and perhaps palato-pharyngeus. These all con- 
tract strongly from the periphery towards the centre point 
of the oro-pharynx. The buccinator muscle is also drawn 
strongly inwards, and the floor of the mouth upwards 
(Fig. 5). The pterygo-maxillary ligament, to which is 
attached the superior constrictor and the buccinator 
muscles, and which is itself attached to the posterior 


end of the internal oblique line of the lower jaw, is also 
drawn inwards and backwards. These muscles all act 
directly or indirectly upon the growing ends of the 
maxillae. If a skiagram of the maxillae at this age be 

Fig. 6. — Skiagram of the Jaws of a Child aged Four axd 
a Half Months. 

[From Symington and Rankin's "Atlas of Skiagrams," by per- 
mission of Messrs. Longmans, Green and Co.) 

examined (Fig. 6), it will be seen that the terminations 
of the maxillary bones correspond at this period with 
the position of the first permanent molars, and it is 
precisely in this position, when these teeth have erupted. 


that the narrowing of the arch is most marked.* 
Other muscles brought into continuous action by such 
sucking are the genio-glossi and genio-hyoglossi. thus 
tending to pull the lower jaw back (or prevent its 
forward development). 

Compare such action with that occurring in sucking a 
normally-shaped nipple. In the latter case the " teat " 
does not enter the mouth very far. and the whole action 
is one of semi-mastication rather than " sucking." The 

Fig. 7. — Diagram of Natural-shaped Teat. 

Designed to imitate the shape and resiliency of the natura 1 
breast. It can only be used in the anterior part of the child's 

A, Thick " core " of soft rubber (solid) ; E, concave disc of hard 
rubber vulcanized to A ; C. large rubber teat stretched over 
A and B, and gripping B at D by its thickened edge ; E, ivory 
or metal ring. 

lower jaw is constantly moving, and the proper muscles 
of mastication are being used and developed. 

In natural suckling the action is one of expression by 
the lower jaw as much as sucking with the mouth. In 
order that this natural function may be imitated as 

* Dr. J. Stoddart Barr (" The Effects of Chronic Xasal Ob- 
struction during Childhood upon the Growth of the Teeth and 
Jaws," British Dental Journal, 19 10, p. 480) has also noted the 
fact that it is not until the " large permanent teeth " erupt that 
constriction of the jaws is observed in cases associated with nasal 


nearly as possible. I have devised a " dummy " or 
" comforter " which should have all the advantages, 
with none of the disadvantages, of the ordinary article. 
The accompanying diagram (Fig. 7) represents its con- 

The old-fashioned long-teated, long-tubed bottles for 
the artificial feeding of infants should never be used. It 
is far better from a dental point of view alone to use no 
kind of bottle at all. but to encourage and enforce as 
far as possible the natural suckling of infants. But if 
this is impossible,, then the best kind of bottle to be 
used is one with a wide neck, like a jam-jar, and 
having a very large teat resembling in shape the natural 
breast. One such bottle at least is on the market ; even 
this, however, is not without defect. The " nipple " 
is far too small. It represents rather the nipple of a 
functionless, atrophic breast than that of a functioning, 
secreting breast. 

B. The Condition of the Deciduous Teeth. 

Although citing this as a cause of caries may seem like 
begging the question, yet undoubtedly untreated or mal- 
treated disease of the deciduous teeth tends to increase 
the susceptibility to caries in the permanent teeth. Caries 
of the approximal surfaces of the deciduous teeth allows 
them to come together (see Fig. 8). The cavity rarely 
remains as a space. The force which brings this about 
is probably the developing or erupting first and second 
permanent molars at the back of the jaws. Thus room 
is found for these teeth at the expense of that portion 
of the jaw already developed, instead of the jaws de- 
veloping backwards in order to accommodate them. 
The result of this is that the permanent premolars, 
canines, and often lateral incisors, are forced to erupt 
in irregular and crowded positions, and the jaws as a 
whole are smaller than normal. Deciduous teeth, too, 
may be retained too long or extracted too soon. In 


either case, irregularities in the permanent teeth are 
sure to result. 

Alveolar abscesses may develop in connection with the 
temporary teeth, and these frequently cause structural 
defects in the enamel of the permanent teeth, and may 
thus render them more susceptible to caries. It is 
therefore of the very highest importance that particular 

Fig. S. — Model of a Lower Jaw, illustrating the "Loss 
of Space " which occurs owing to Caries of the 
Deciduous Teeth. 

Note the manner in which the second deciduous molar on the 
leit has encroached on the space originally occupied by the 
first deciduous molar. 

care and attention should be paid to the preservation of 
the deciduous teeth by the methods which have been 
already and which are to be hereafter described. 

A point which has struck me in the examination of 
the skulls of children of uncivilized races is the marked 
attrition and evidence of much use in the deciduous 


teeth. Evidently even the very little children used 
their teeth for their proper purpose — the mastication of 
fibrous (and, as will be shown, acid) substances — and 
consequently there are never any signs of irregularities 
or crowding of the teeth, and no trace of caries. 

C. Adenoids. 

The presence of adenoid vegetations in the naso- 
pharynx has been supposed to lead to a contracted con- 
dition of the jaws and irregularities in the teeth, and 
hence to favour the development of caries. 

Colyer (loc. tit.) has shown that the presence of 
adenoids in eighty-two cases was associated with an 
average contraction, in the deciduous molar region, of 
2-12 millimetres, and of 1-49 millimetres between the 
first permanent molars. Such cases showed constantly 
a crowding of the incisor teeth also. 

Mackenzie* also has examined 222 adenoid cases at 
the Central Throat and Ear Hospital, and finds that of 
these 43-2 per cent, had normal palates, 397 per cent. 
had " high " palates, and 17-1 per cent, were " Gothic " 
(high and laterally compressed) — that is to say, 43*2 per 
cent, were normal, and 56-8 per cent, more or less con- 

Thus, there would seem to be an undoubted associa- 
tion between " adenoids " and contracted jaws, but as 
to which of these is cause and which is effect is not 
so easy of determination. Personally I am strongly 
inclined to the opinion that the contracted jaws are 
more frequently to be regarded as the cause, and the 
adenoids as the effect. 

We have already referred to the fact that for the 
normal development of the jaws normal function is (in 
the absence of a very strong hereditary force) absolutely 
necessary, and that the avoidance of this normal func- 
tion by the (?) mastication of soft " nutritious " food 

* British Medical Journal, 1906, p. 989. 



must lead to under-developed, narrowed dental arches 
and jaws. This is not without its effect upon the nasal 
cavities, as will be seen in Fig. 9. 

The nasal cavities become constricted both in width 
and depth, and, further, if the nasal septum has an 
inherent tendency to growth, this can only occur by its 
becoming deflected. The result is that nasal breathing 
becomes more difficult, and impossible in any slight in- 
flammation of the nasal mucous membrane. The patient 

Fig. 9. — Diagrams illustrating the Effect of Narrowed 
Dental Arches upon the Nasal Cavities. 

I. represents contracted jaws and potential adenoid nasal fossae ; 
II. represents the normal. It will be seen that, whilst 
the distance A to C is much less than A' to C\ the distance 
A to B is equal to A' to B' — i.e., the palate has developed 
upwards at the expense of the nasal cavities. 

acquires the habit of mouth-breathing, and adenoids 
develop in the stagnating nasal cavity. 

This appears to me a much more reasonable and 
logical sequence of events than that the width of the 
jaws should be influenced by the passive presence of 
new growths in the nasal cavities. 


On the contrary, growths in general cause expansion 
(or absorption) of bones. 

The expanding force of the normal passage of air 
through the nasal cavities is infinitesimal compared 
with that exerted normally by the muscles of mastica- 
tion, and any diminution of the latter forces is much 
more likely to be followed by obvious effect than is total 
elimination of the former. 

Again, it is contended that blocking of the nasal air- 
ways causes contraction of the dental arches by pro- 
moting mouth-breathing — that is to say, by the upper 
and lower teeth not coming into contact ; but this is 
the normal position of the jaws and teeth when mastica- 
tion is not being performed, and therefore cannot be 
put forward as a cause of the contraction. 

I do not pretend to think that narrowed jaws depen- 
dent on deficient mastication are the sole cause of 
adenoids ; but when the two are associated, I do think 
that the adenoids are secondary to the condition of the 
maxillary bones. There is no doubt, however, that 
mouth-breathing is deleterious to the teeth, and favours 
the occurrence of caries. It tends to keep the mouth 
dry and negative the beneficial effect of the circulation 
of the saliva ; and it also must promote a constant and 
enormous increase in the bacterial flora of the mouth by 
the inhalation of dust-laden air, which always contains 
numbers of fermentative bacteria — the exact varieties 
which are principally concerned in the early stages of 
caries. It is therefore obvious that adenoids may be a 
factor in the production of carious teeth, and should 
therefore be eliminated, by hygienic and educational 
means preferably, as early in the child's life as possible. 

Heredity and Dental Caries. 

There must be in all growth and development two 
fundamental forces at work — firstly, that mysterious 
force which we know as heredity, because of which off- 


spring tend to resemble their parents even in minute 
details ; and, secondly, the resultant of all those external 
forces which are continuously acting upon an organism, 
and known as environment. 

Now, these two forces may act in unison, may both 
tend in the same direction, or they may be forces acting 
in different directions, and thus oppose each other. If 
the first condition obtains, then the hereditary charac- 
teristics tend to be perpetuated, and may become more 
marked. If, however, the second condition be present, 
a number of variations are possible. 

Logically, of course, if the two forces of heredity and 
environment are equal and opposite, the organism ceases 
to exist, and for the present argument this variation 
does not concern us. But if the forces of environment 
oppose the hereditary tendency to a lesser extent, then 
more or less modification of the hereditary morphology 
and structure of the organism will be brought about. 
And it is largely a question of the relative strength of 
these two forces that determines whether an offspring 
which exhibited the normal characteristics of its race 
strongly in infancy will continue to do so during growth 
and development towards adult life, or will during this 
period, when environmental forces are continuously 
becoming more strong, show modifications of, or depar- 
tures from, the original characteristics. These modifica- 
tions may be brought about either by an increase of the 
environmental forces or by a decrease in " hereditary 
force," or by a combination of both. 

Thus the tendency of the force of heredity is to pro- 
duce jaws well shaped in paraboloid curves, teeth of a 
certain size and shape, and regularly arranged in the 
jaws. But, as we have seen, habit and environment 
(more particularly expressed in the dietary of the indi- 
vidual) may profoundly modify the shape and size of 
the jaws. In very early childhood, during the period 
of deciduous teeth, the forces governing the growth and 
development of the jaws are largely hereditary, and con- 


sequently the jaws are usually well formed and the teeth 
regular in arrangement. 

During this period the crowns of the permanent teeth 
are being developed, and hence heredity commences (at 
least) to form teeth of the normal size. 

The two forces of heredity and environment then come 
into opposition. Heredity demands a full-sized tooth ; 
the forces of environment, acting on the jaws, limit the 
available space. The result is a compromise. The jaws 
develop a little in an attempt to make room for the 
teeth, and, as will be shown, the teeth are restricted in 

An instance of heredity and environment acting in 
unison is that of uncivilized races. Both forces tend to 
produce well-shaped jaws and teeth. Instances of en- 
vironment proving too strong for heredity are only too 
common, but an interesting instance of heredity over- 
coming environment is afforded by the following case, 
like which there are doubtless many more : 

An Englishwoman had two husbands, the first an 
Englishman, and the second a negro. The children of 
the first marriage had the usual jaws and the teeth of 
civilized races ; the children of the second marriage were 
brought up with the other children, with identical en- 
vironments, yet they possessed well-shaped jaws and 
sound teeth. 

This influence of a slight balance of hereditary force 
over environmental forces has been thrust upon my 
attention during the last few years when I have had 
occasion to examine the teeth of a large number of 
" orphanage " children — children in whom the force of 
environment has been identical for all practical purposes, 
and yet whose jaws and teeth showed wide variations 
as to shape, disposition, and incidence of caries. This 
is only to be accounted for by the preponderance in 
some cases of hereditary force over environment. 

Further, there would seem to be every reason for 
believing that the loss of " hereditary force " tends to 


be transmitted, particularly when the forces of environ- 
ment are not acting in conjunction with it. Or, ex- 
pressed otherwise, the possession of strong, well-formed 
jaws and regular teeth cease to be of paramount ad- 
vantage to the individual in the mastication of food 
(thanks to the services of the dental surgeon and to 
the ready acquisition of soft " supernutritious " food), 
and so, like all other organs or organisms in Nature 
which have become more or less functionless, tend to 
be reproduced in offspring in a correspondingly de- 
generate condition. Thus in any particular case we 
may have a " negative " environmental force combined 
with a " negative " hereditary force, producing an ex- 
aggerated smallness of the jaws and crowding of the 
teeth — a condition difficult of immediate prophylactic 

The application of an environmental force may pos- 
sibly accomplish much in early life, but would be more 
certain of attaining a normal result if applied for one or 
two generations. Such a condition could, of course, be 
combated by the application of sexual selection, but in 
civilized communities of the human race parents are not 
selected on account of their physical characteristics, but 
increasingly for economic and social reasons alone. 

The resultant of the same two " forces " is, of course, 
expressed in a similar manner in the growth and develop- 
ment of the soft tissues — i.e., in the muscles of mastica- 
tion and the salivary glands. The effect of the former 
upon the jaws and teeth has already been noted, and 
the effect of variations in the latter upon the teeth will 
be considered subsequently. 






Much has been written and much valuable work accom- 
plished on the structure of the enamel of teeth, but all 
histologists and authors seem to have confined their 
attention to the minute structure of the body of enamel. 

Even Miller, 1 in his researches on the pathology of 
caries, seems to have omitted the surface structure of 

Leon Williams, 2 whose name is inseparably connected 
with the development and structure of enamel, touched 
on the subject but briefly when demonstrating the 
presence of a film on the surface of enamel, especially 
on carious enamel. 

Tomes 3 refers to the subject only in the following 
words : " The cap of enamel on a human tooth is of 
varying thickness, being thicker in the neighbourhood 
of the cusps than elsewhere. Its outer surface is often 
finely striated, the striae being transverse to the long 
axis of the crown. In addition to this fine striation, 
there may be a few deeper and more pronounced grooves 
or pits, which are pathological, and are marks of checks 
in development more or less complete." 

Hopewell Smith 4 states briefly : "Surface smooth, 
shiny, sometimes traversed by tiny vertical or horizontal 
depressions, occasionally scrobiculated, and normally 
deeply fissured in premolars and molars, and pure white 
in colour. When fractured, pure white, non-lustrous." 

49 4 


That the minute structure and physical characteristics 
of the enamel surface in normal and abnormal condi- 
tions is worthy of consideration must be obvious when it 
is remembered what an important role this must play 
in the question of immunity or susceptibility to dental 

It is at the enamel surface alone that the process of caries 
is able to be prevented or checked, either naturally or by 
artificial means. This point being passed, the total 
destruction of the tooth is merely a matter of time 
(except in those comparatively rare cases of "arrested 
caries "). 

An investigation of the surface of the enamel of a 
large number of teeth has therefore been made, some 
of the results of which it is proposed to deal with here. 

Over 1,000 teeth of civilized and savage races have 
been minutely examined microscopically and physically, 

For the purpose of this investigation teeth were 
divided into three empirical or clinical groups : 

i. Native teeth, comprising those of uncivilized races 
but little, if at all, afflicted with caries. 

2. Sclerotic teeth, comprising that clinically well-known 
class of teeth which are characterized by their " hard- 
ness," usually yellow colour, and immunity to caries. 

3. Malacotic teeth (Gr. //uAo.Kos = soft), also a well- 
recognized clinical variety characterized by their com- 
parative " softness," whiteness, and susceptibility to 

As stated above, these divisions were accepted em- 
pirically, though up to the present there has been no 
scientific basis for such a classification. In fact, the 
experiments of Tomes 5 and Black 6 on the composition 
and physical characteristics of enamel go rather to 
negative any such classification, seeing that they agreed 
in finding no appreciable difference of density, structure, 
or composition, between "soft" and "hard" teeth, or, 
at least, not such as would lead to their vaning pre- 
disposition to caries. 


These views are endorsed by Leon Williams 7 and by 
Kirk. 8 Nevertheless it is a convenient clinical classifi- 
cation, and one which the writer believes is justified by 
the results hereafter to be described. 

1. Histological Examination of the Enamel Surface. 

In this branch of the inquiry, the first undertaking 
was a thorough examination of the enamel surface of a 
large number of all classes of teeth under the microscope 
by reflected light. 

The difficulties of lighting and staining were at first 
considerable, and, after trying and abandoning many 
other methods, the following simple method of staining 
was adopted, as giving the most satisfactory results : 

The tooth to be examined is first washed in water 
and dried, and then the surface well cleaned with xylol 
or ether and alcohol. The stain used is graphite. This 
is applied dry on a soft pad (or the finger), and excess 
removed with a piece of soft smooth rubber. The result 
of this treatment being that with moderate pressure the 
graphite is rubbed into all depressions in the enamel 
surface, whilst it is removed from all elevations ; conse- 
quently, depressions are stained black, and elevations 
remain white. Whereas with very light staining, in 
some cases, the elevations are stained, and the depres- 
sions remain their normal colour. 

By this method and by the correct interpretation of 
what is seen a great deal may be learned of the minute 
structure of the enamel surface. 

From such an examination, it is concluded that the 
surface of enamel is not normally smooth in human teeth 
nor in many animals. It is in its normal condition 
traversed by minute ridges separated from each other 
by corresponding " furrows " which run parallel to 
each other in a direction at right angles to the long 
axis of the tooth. 

These horizontal lines are in some cases large enough 


to be visible to the naked eye, and must have been 
noticed occasionally by many who, like myself, thought 
at first that they were either caused by attrition or were 
a microscopic form of hypoplasia ; yet in all the teeth 
examined only one failed to show any sign of these ridges 
and furrows. And it is significant that this exception 
was an abnormal tooth — a lower molar with a crown 
elongated antero-posteriorly to twice its normal length, 
and with an exceedingly rounded, stunted, and single 

Such horizontal lines (or ridges and furrows), for 
reasons subsequently to be described, I have termed 
" imbrication lines." 

I have examined microscopically the teeth in every 
skull in the Anthropological Museum of this University. 
This collection of skulls is of various races all more or 
less uncivilized, including Fijians, Australian aborigines, 
Maori, Moriori, Rarotongans, inhabitants of New Guinea 
and New Hebrides, Negro, Hindoo, Chinese, Mexican, 
and Anglo-Saxon. These also, with only one exception, 
all showed evidences of minute imbrication lines on the 
surface of the enamel. 

In all teeth the ridges are widest and the furrows 
deepest at a point two-thirds of the distance between 
the neck and the occlusal surface, or cutting edge. From 
this point they gradually diminish in size upwards and 
downwards. At the neck of the tooth they are much 
more numerous in a given space, but are very much 
finer and less marked. They extend towards the oc- 
clusal surface in an unworn tooth, and do not here 
diminish so much in size, but they do very greatly in 
frequency. They also naturally rapidly disappear from 
this situation when the tooth has been subject to masti- 

Fig. 10 shows the appearance of the " normal " 
enamel surface of a malacotic tooth at a point two- 
thirds of the distance between the neck and the occlusal 
surface (treated by the graphite method and viewed 



Fig io. — Imbrication Lines on a Malacotic Tooth, from the 
Distal Surface near the " Point of Contact." 

I * 

Fig. ii. — Imbrication Lines on a Malacotic Tooth, near 
the Cervical Region. 


by reflected light under the microscope). Fig. n 
is a photomicrograph from the same tooth at a point 
close to the neck. Fig. 12 shows the character of the 
imbrication " lines " in a Maori tooth. The average 
distance apart of these lines was, on measurement with 
the micrometer, found to be o - oi millimetre in the 
cervical region, and o - i millimetre at a point half of 
the distance between the neck and occlusal surface. 

Fig. 12. — Imbrication Lines from the Distal Surface of 
a Maori Molar. 

With regard to the accompanying photomicrographs, 
it should be pointed out that the surface to be dealt 
with is both irregular and convex, and that it is there- 
fore impossible for the whole of the field to be in focus 
at one and the same time. 

2. The Enamel Surface in Outline. 

Sections of enamel from teeth with the lines well 
marked show with accurate focussing the ridges and 


furrows in outline. Fig. 14, which is the same magnifi- 
cation as Fig. 10, and viewed with reflected light, shows 
this. Fig. 15, which is taken from the same section, 
but viewed by transmitted light, shows this structure 
even more markedly. The fact that the " outline " of 
the surface lines is not easy to demonstrate by trans- 
mitted light is due to the thickness of sections of enamel 

Fig. 13. — Unstained Stride on the Enamel Surface. 

These are not " imbrication " lines, and are possibly the outcrop 
of Schreger's lines. They can only be seen on highly 
polished surfaces and facets. 

interfering with accurate focussing ;* whereas by examin- 
ing a section of any thickness by reflected light, only 
one surface is illuminated, and thus all is accurately 

* The lower edge of the section usually throws a shadow 
which obscures the detail of the upper edge, and the substage 
lighting requires adjusting to avoid this. 

Fig. 14. — Imbrications in Outline. 

Note the relationship of the striae in the enamel to the 
imbrications (low power, reflected light). 


Fig. 15. — Imbrications in Outline. 
(High power, transmitted light.) 


3. Curvature of the Enamel Surface. 

In examining the teeth of native races, the enamel 
surface has the appearance of being more curved than 
that on the teeth of modern civilized races ; also it seems 
to arise more abruptly at the cervix in the former class 
of tooth, resembling the abrupt ridge on the teeth of 
some carnivora and on human deciduous teeth. 

These conditions, although not constant, were suffi- 
ciently frequent to suggest the cutting of sections to 

Fig. 16. — A, Vertical Section of Enamel of European 
Molar Tooth ; B, Vertical Section of Enamel of 
Maori Molar Tooth. 

compare the curvatures and their causes. As a result 
the causes of these conditions were found to be totally 
different. This will be seen on reference to Figs. 16, 
17, and 18. 

In the permanent European tooth it will be seen that 
the enamel rises slowly and gradually from the cervix, 
whereas in the " native " tooth (Fig. 16) it rises much 



Fig. 17. — A, Vertical Section of Enamel of European 
Permanent Molar ; B, Vertical Section of Enamel 
of European Deciduous Molar. 

Fig. 18. — Vertical Section of the Molar Tooth of a Dog, 


more abruptly ; and this is occasioned solely by the 
increased thickness of the enamel. 

Fig. 17 represents a permanent and a deciduous tooth 
mounted side by side. It will be seen that there is a 
similar abrupt rise of enamel from the cervix of the 
milk-tooth as in the native tooth, but that it is caused 
entirely by an increased thickness of the dentine, as if 
the dentine germ had bulged out at that point during 
development, and the normal thickness of enamel formed 
over it. 

Fig. 18 is a section of the molar of a dog, and shows a 
similar conformation to that of the human milk-tooth. 

The effect of this difference in curvature and thickness 
of enamel in the cervical region is important, in that it 
obviously, in the native tooth, diminishes the amount of 
interdental space, and therefore diminishes also the 
amount of carbohydrate which might lodge there. In 
the European teeth the space is greater and the enamel 
is more imbricated, and so food would lodge in greater 
quantity, and would also be more difficult to remove 
by natural means. It will be shown later that this 
diminished curvature and increased imbrication are 
probably intimately connected and arise from a common 
cause, and that the remedy lies in eliminating this 
common cause. 


1 Miller : Micro-Organisms of Human Mouth : Dental Cosmos 

2 Williams, Leon : Dental Cosmos, 1898. 

3 Tomes, C. S. : Dental Anatomy, p. 20. 

4 Smith, Hopewell : Histology and Pathohistology of the 
Teeth, p. 20. 

5 Tomes, C. S. : Journal of Physiology, 1896, Xo. 3. 

6 Black : Dental Cosmos, 189*5, P- 4 T 7- 

7 Williams, J. L. : Dental Cosmos, 1898. 
3 Kirk, E. C. : Dental Cosmos, 1903. 


Graphic Representation :: the Enantel Sttriace. 

The methods hitherto described of examining and 
recording the variations in the enamel surface and in 
the thickness of the enamel require the expenditure of 
a considerable amount of time upon each tooth ; more 
especially is this so when sections of the enamel have to 
be cut and examined by transmitted light. It therefore 
seemed necessary that, if a large number of teeth were 
to be examined and compared, some rapid and accurate 
method for the purpose, and for the purpose of mechani- 
cally recording the variations, was absolutely necessary. 

To this end an assemblage and modification of appa- 
ratus used in experimental physiology was made, and the 
specialized form which it took may be called an 
lt odontography" 

The apparatus may be best explained by reference to 
the accompanying diagram (Fig. 19). 

A is the usual revolving drum used in experimental 
physiology (the surface of the cylinder being covered 
with smoked paper). 

B is the usual form of stand, with a revolving upright 
and movable platform C. To this platform is hinged 
very delicately a long and very light wooden lever. D ; 
as a rule this was at least 2 feet in length. 

At E on the lever is fixed a needle, the point of which 
impinges upon the surface of the tooth to be examined. 
The tooth is fixed by wax to a small carriage. F, on four 
wheels, which runs between rails on the platform. 




The carriage is drawn forwards by means of a string 
attached to its front part, and passing under the pulley 
G and over H on to a large receiving pulley, K, which is 
fixed to the revolving axle of the cylinder. Thus, when 
the drum revolves, the tooth is drawn forward mechani- 
cally, and its rate of movement always bears the same 
ratio to the rate of movement of the drum. By having 
several receiving pulleys of various sizes, the rate at 

Fig. 19. 

-Apparatus arranged for recording 

which the tooth passes under the needle can be varied 
as desired. 

To the back of the carriage is suspended a weight, in 
order that the string in front may always be taut. It 
is also necessary, usually, to suspend a small weight from 
the lever in front of the needle, in order to avoid instru- 
mental vibration from being recorded. 

In this manner, when the drum is revolved, the tooth 
in passing under the needle raises the latter or allows it 



to fall, to a very small extent, according as there are 
elevations or depressions on the surface of the enamel. 
Owing to the length of the lever these oscillations are 
greatly magnified, and are recorded on the smoked paper 
as curves and waves. Such a record may be most 
appropriately termed an "odontogram." An odonto- 
gram records chiefly two things : 

i. The presence or absence of imbrication lines. 

and the extent of their development. 
2. The thickness of the enamel. 

The former is obvious ; the latter, perhaps, may not be, 
and will be explained shortly. 

Figs. 20 and 21 are the odontograms of perfectly sound 

Figs, jo and j 

-Odontograms of Malacotic Teeth. 

and typically malacotic teeth with well-marked imbrica- 
tion lines. From i to 2 represents the cement. 2 is the 
neck. 2 to 3 is the surface of the enamel up to the 
bulb of the crown, and 3 to 4 from the bulb to the 
occlusal surface. The secondary waves represent the 
imbrication lines, and it will be noticed that they are 
most marked in the first half of the primary curve. The 
high peak of some of the secondarv waves is probablv 
due to instrumental vibration — just as in a sphyg- 



mogram — and the needle has therefore at this point 
failed to record several imbrications. 

The odontograms of typical Maori teeth are shown in 
Fig. 22. It will be noticed that they differ markedly 
from those of the malacotic teeth. In the first place, 
the shape of the primary curve is quite different, and, 
secondly, the frequency and extent of the secondary 
curves are much diminished. This latter means, of 
course, that the imbrication lines are much less marked 
on the enamel surface, but that they are present. 

Fig. 22. — Odontograms of Maori Teeth. 
x = commencement of enamel. 

The difference in the primary curve is caused by the 
difference in the curvature of the enamel surface. The 
most obvious difference is the very marked and abrupt 
rise at the commencement of the enamel ; it is this 
abruptness of rise in this position which is a measure of 
the thickness of the enamel on the side of the tooth (but 
especially on the mesial and distal surfaces). This 
applies only to human permanent teeth ; a similar 
abrupt rise is noticed in the odontograms of human 


deciduous teeth and of the teeth of carnivora, but, as 
we have already seen (Figs. 17 and 18), it is due in these 
cases to a bulging out of the dentine. The actual height 
of the top of the curve bears no relationship to the 

Fig. 23. — Odontograms of Deciduous Teeth. 

Fig. 24.— Odontogram of a Sclerotic Tooth. 

thickness of enamel, since this can be artificially altered 
by changing the position of the tooth on the carriage ; 
but if a vertical line be dropped to the base line from 
the highest point of the curve, and the distance then 


measured along the base line from the point where the 
enamel begins to the vertical line, it may be said that 
the thickness of the enamel is inversely proportional to 
this measurement. 

The odontogram of a sclerotic (European) tooth is 
shown in Fig. 24. It will be noticed that it is inter- 
mediate in type between the malacotic and " native " 
tooth ; the rise is a little more abrupt than in the mala- 
cotic tooth, and the imbrication waves are a little less 

Fig. 25 represents the odontograms of a dog's teeth 

Fig. 25. — Odontograms of a Dog's Teeth. 
A, Canine tooth; B, molar tooth. 

An abrupt rise is noticed, but there is a complete absence 
of imbrication waves. 

A considerable number of odontograms have been 
obtained in this manner, and they all conform, with 
minor exceptions, to the above types. 

In using the odontograph, it is necessary, of course, 
for the sake of comparison, to know (1) the length of the 
lever, and (2) the ratio of the speed of the drum io that 



of the carriage, and only those odontograms obtained 
under similar conditions can be compared. For the 
odontogiams here reproduced a lever of 2 feet in length 
was used, and the carriage was arranged to travel at 
exactly half the speed of the drum. 

By means of this graphic method, therefore, are again 
confirmed the differences previously observed between 
the various classes of teeth. 



That the imbrication lines are not artifact or acquired 
is proved by the facts (i) that they are best marked on 
unworn surfaces and on unerupted teeth, of which a 
considerable number, both native and " European," have 
been examined ; and (2) by their presence on those teeth, 
native and otherwise, which have a covering of salivary 

(Fig. 26, a photomicrograph from the naturally 
polished surface of a canine tooth, shows " artifact " 
lines, which are obviously of a very different nature.) 

It is inconceivable, from their practically universal 
presence, that they are due to any hypoplastic defect. 
They therefore must be regarded, at least in " native " 
teeth, as physiologically developed structures. 

It is of importance in this connection to note the very 
close relationship between the imbrication lines and the 
"striae of Retzius " ; this is shown quite distinctly in 
Figs. 14 and 15. 

Fig. 14 being photographed by reflected light, the 
striae of Retzius appear light (but it will be noticed that 
Schreger's lines are dark). 

In Figs. 15 and 28 they are of the usual dark colour. 

It will be noticed that each ridge appears to be 
formed by the termination of one of the "striae of 
Retzius," and that each furrow or depression coincides 
with the termination of a light striation of enamel 
separating the dark striae. Furthermore, both the fre- 



quency and length of the surface ridges would seem to be 
directly dependent on the angle of incidence which the 
striae make with the surface. 

Thus in the cervical portion the angle of incidence is 
greater, and the surface ridges are both numerous and 
short ; towards the occlusal surface the angle of incidence 
becomes progressively less, and the ridges longer and 
fewer, until the striae become parallel with the surface. 



***—' * ~~ 

->V - "- 


Fig. 26. — Artifact Lines ox Canine Tooth, " stained 
with Graphite. 

and the ridge ceases to be distinguishable as such, but 
forms part of the general contour of the tooth (Fig. 27). 
And, conversely, when the ridges cease to be apparent, 
the striae of Retzius also cease to be so marked, although 
remaining distinctly visible. Again, in those teeth, animal 
and human, from which the striae of Retzius are absent, 
the imbrication lines are also absent. The absolute 
interdependence of imbrications and striae upon each 
other is thus apparent. 


I have therefore termed these lines on the enamel 
surface imbrications or imbrication lines, since the 
whole appearance is so suggestive of stratification and 
imbrication as to give reasonable ground for the belief 
that this is the method of the formation of ridges, 
furrows, and striae. This is in accord with Kolliker's and 
WalkofF s belief that all striation in enamel is due to the 
deposition of lime salts in strata. It is opposed to the 

Fig. 27. — Cessation of Imbrication Lines when Striations 
become Parallel to the Surface : Coronal Region of 
Unworn Molar Tooth. 

theory that the striae of Retzius are due to pigmentation 

Leon Williams has proved that enamel rods pass 
through some varieties of striae without break in con- 
tinuity. This latter is undoubtedly true of some striae 
(those in the occlusal part of the enamel especially 
which do not make any outcrop on the surface), but 
does not affect the argument, and is only analogous to 



what is frequently observed in dentine and cement 
when increments are added. 

If the striae of Retziuswere due to pigmentation, they 
should appear the same both by reflected and trans- 
mitted light — i.e., dark; but, as has been pointed out, 
by reflected light they appear white, and the inter- 
mediate substance dark. This can only be accounted 
for by the striae possessing a greater optical density. 

Difference in physical density may be proved by 

Fig. 28. 

-Stride and Imbrications : " Point of Contact 

examining suitable sections by polarized light. The fol- 
lowing simple experiment gives an analogous probability 
that the " brown " lines are due to an increase in density. 
A number of overlapping films of pure " Chinese white " 
(zinc oxide) and water were painted on a microscope- 
slide, and examined under the microscope. The result 
is a brown striation, in appearance closely resembling 
that of the brown striae of Retzius when viewed by 



transmitted light (Fig. 29) ; but by reflected light the 
brown striation becomes white, and the intervening film 
dark (Fig. 30). These two photomicrographs were made 
without taking the slide from the stage. 

We are therefore bound to conclude that such 
" striation " in enamel is due to physical differences in 
refraction, and not to pigmentation at all (except in 
pathological cases). 

There appear to be two varieties of lines or stria — one 


Fig. 29. — "Brown Striations " (\) produced by Over- 
lapping Films of Chinese White. 

which is caused by the granularity or increased optical 
density of the prisms themselves, and a second which 
is caused by an increased amount of differing disposition 
of the cement substance. 

The former variety are found chiefly in the occlusal 
half of the enamel, and constitute those striaa which run 
more or less parallel to the surface of the enamel, and do 
not make any actual " outcrop " on the surface. 


These stride are caused entirely by an increased optical 
density or granularity of the prisms themselves ; they 
are of varying intensity, thickness, and frequency, and 
their margins are comparatively ill-defined. 

The second variety of striae are seen mostly in the 
cervical portion of the enamel, and constitute those 
striae which make an outcrop on the surface. There 
may be merely an increased amount of cement substance 


Fig. 30. — The Same as Fig. 29, but viewed by Direct Illu- 
mination. The " Brown Strle " have become White. 

on each side of the prisms, corresponding to a constriction 
of the latter, or the cement substance may pass right 
across the prism in a narrow band. This can only be 
observed by fine focussing in sections not too thin, and 
hence cannot be adequately represented in a photograph. 
It is frequently stated that this is only apparent when 
the section is cut at a " certain angle " ; this I have not 
found to be so. It would, I think, be truer to say that 
it only occurs in enamel from a " certain position " — 


i.e., the cervical half or one-third, and then only near the 
surface. Here, too, after this variety of striae the enamel 
prisms frequently suffer deflection from the original 
course, and in human teeth at least this deflection is 
practically always towards the occlusal surface — i.e., 
in the direction in which there is most room in the 

Horizontal sections do not show any lateral deviation 
of the prisms ; neither on fine focussing through thicker 
sections are the prisms seen to deviate in more than one 


The only rational solution of such appearances is that 
imbrications and striations of all varieties are to be 
regarded as evidence of checks in the secretive function 
of the ameloblasts. 

As regards the nature of the check to the ameloblasts 
above referred to, the writer believes it to be due to the 
pressure of the bony walls of the crypt in which the tooth 
is developing — i.e., the resultant of two forces of evolu- 
tion : 

1. The hereditary tendency of the ameloblasts to 
continue functioning to a certain definite extent. 

2. The limiting force of environment, expressed as a 
diminution in the size of the jaws — i.e., the result of 
altered habits of diet, and also to some extent of natural 

The cap of enamel commences to be formed over the 
' ' cusp ' ' of the dentine, and gradually extends down to the 
cervix, but the full complement of enamel is laid down 
at the occlusal surface long before it is complete in the 
cervical region ; hence it is obvious that atrophy of the 
ameloblasts in the occlusal region must occur, whilst 
those in the cervical region continue their function. 

This process of atrophy of an increasing number of 
" occlusal " ameloblasts and active secretion by a 
decreasing number of cervical cells must continue until 



development is complete. Reference to Fig. 31 explains 

this diagrammatically. 

Enamel formation commences at A, and continues 

concentrically until B— C is reached ; the cusp of the 

occlusal surface is then fully formed, and the amelo- 

blasts atrophy in that region — i.e., from B to D — but 

continue to function from C to D. 

The fact of a number of cells of the enamel organ 

thus atrophying will have an effect on the remainder. 

If atrophy of a portion of an organ be gradual, the 
effect is probably to increase the 
functional power and secretion of 
the other cells ; if more sudden, as 
it would be by the ameloblasts 
being driven against the unyielding 
walls of the crypt, the check would 
be communicated to the rest of the 
organ — i.e., the remaining amelo- 
blasts. The result would undoubt- 
edly be the formation of enamel of 
an altered density, or a sudden 
diminution in the size or cessa- 
tion of the prisms — both of which 
would give a well-marked line or 
sis as to Origin of striation. 
Stride and Imbrica- The nr ranu l ar it y or increased 
tion Lines. . , c ' ., j , 

optical density 01 the prisms is 

probably an expression of a minor check to develop- 
ment, and, as we have seen, this variety of striae is 
only seen in that part of the enamel which is formed 
before the occlusal portion has reached its maximum 
development — i.e., when the disproportion between the 
requirements of the developing tooth and the available 
space has not become acute. 

The other variety of striae occurring after the latter 
event is caused by a more sudden and acute atrophy, 
and hence even those ameloblasts which do not atrophy 
temporarily cease to function to their full and normal 

Fig. 31. — Diagram to 
explain hypothe- 



extent, the result being a marked constriction in the 
prisms, or a line of cement substance passing obliquely 
across the prism. 

Referring once more to Fig. 31, the process of atrophy 
occurs again at E and F; i.e., the cells between these 
two points atrophy, and so give rise to a well-marked 
ridge of enamel on the surface where calcification is 
continued, and a striation passing inwards as far as the 
dentine. That is to say, according to 
this hypothesis the distance between 
"ridge" and "furrow" (1 to 2 in 
Fig. 32) is a measure of the number 
of cells which atrophied ; and the 
depth of each " ridge " (2 to 3 in 
Fig. 32) is a measure of the time be- 
tween each " atrophy." Both of these 
diminish towards the cervix, where 
either less enamel is " required " or 
there is less room for its develop- 

It would thus appear that an atrophy 
of ameloblasts occurred fairly regu- 
larly. There may be, too, some sig- 
nificance in the fact that the depth of 
each imbrication or ridge (2 to 3 in 
Fig. 32) approximates very nearly to 
the length of the ameloblasts in z _ ~ n ~ ber <* cells 
that region; for instance, the former atrophied; 2-3 = 
measure 0-024 millimetre, and the 
latter 0-025 millimetre, in the region 
of halfway between the cervix and the occlusal surface. 

Mention has been made of the presence of imbrication 
lines on the teeth of some of the lower animals. The 
factor which seems to determine their presence or absence 
is the relative length of the circumference of the cervix 
to that of the occlusal surface. If the former exceeds 
the latter, then the imbrication lines are absent ; but in 
proportion as the occlusal surface becomes more flattened 

Fig. 32. — Diagram 
to illustrate 
the Origin of 

time between each 


and of greater circumference, so the imbrication lines 
appear, at first only in the cervical one-third, but 
extending upwards towards the occlusal surface until 
they reach their maximum development in Hylobates 
and civilized man. 

It would appear in cases where imbrication lines are 
absent that the enamel is laid down in the manner 
indicated in Fig. 33, and that no atrophy of occlusal 
cells takes place on account of the relative size and shape 
of the dentine papilla and the den- 
tal crypt; i.e., there is no diminu- 
tion in the size of the jaws, and 
therefore no check to develop- 
ment. In support of this is the 
fact that in those teeth in which 
the imbrication lines are absent 
the striae or indications of atrophy 
of the ameloblasts are also absent. 
This would account for the absence 
of imbrication lines on the de- 

Fig. 33. Diagram ciduous teeth, and also for their 

illustrating the less marked development on "na- 
^™°Fo R °m F a ™n «ve" teeth (cf. Figs. i 2 , 22 , and 

in Teeth whose 23). 

Cervical Cir- l n effect, if this hypothesis be 

G™b E ™n true the facts may be stated thus : 

their Occlusal. The dimensions of the approximal 

alveolar portions of the jaws before 

and whilst the deciduous teeth are in position are 

governed by hereditary forces, but the dimensions of 

the body of the jaws are governed also by the forces 

of environment. If the latter oppose the former, 

then the developing permanent teeth in their crypts 

will be crowded (see Figs. 34, 35, and 36) ; this leads 

to such modifications in their structure as must 

considerably lower their resistance to the attacks of 


The remedy woul dappear to be perfectly obvious : — 

Fig. 34. — Dissected Jaws of a Child, illustrating the 
Amount of Crowding of the Developing Teeth which 
may even occur when there is no caries of the 
Deciduous Teeth. 

The permanent upper lateral incisors are nearly crowded out of 

Fig. 35. — Similar to the Above. 



To increase the beneficial environmental forces by in- 
sisting on active mastication of such food as will develop 

Fig. 36. — Skiagram of Jaws of a Boy aged Six. 

Xote how small is the amount of room available for the develop- 
ment of the permanent premolars. 

From Symington and Rankin's "Atlas of Skiagrams," with 
permission of Mt ssrs. Longmans, Green and < 

the muscles and jaws in a physiological manner, and 
to eliminate those habits which tend to diminish the 
size or alter the shape ol the maxillary bones. 





If the enamel surface of " native " teeth be regarded 
as " normal," then that of civilized and recent teeth 
must as a general rule be regarded as abnormal, for 
in the vast majority of cases the two are materially 

The collection of skulls previously mentioned as being 
examined was in a disarranged state, and thus one had 
no direct reason to know to what race a skull belonged 
until reference was made to the catalogue afterwards ; 
and it was found that one was soon able to distinguish 
native from European skulls merely by the appearance 
of the enamel under the microscope. 

In the teeth of uncivilized races the surface of the 
enamel is lustrous — i.e., reflects much unbroken light 
from its surface ; the imbrication lines are often difficult 
to make out, on account of their being comparatively 
feebly formed, and also on account of the fact that the 
graphite does not adhere to the enamel as it does in 
malacotic teeth, and thus the surface is difficult to 
" stain." 

In a certain number of cases, when the light was 
reflected at the right angle, the outlines of the prisms 
were readily discernible. They were not stained, since 
they are more readily seen without the graphite than 
with it. The " cement substance " merely appears a 
little darker — i.e., does not reflect so much, or absorbs 




more light — than the enamel prisms, just as it does in 
sections of enamel viewed by reflected light. 

In no case could the centre of the prisms be differenti- 
ated. The points that strike one in the examination of 
the enamel surface of the teeth of civilized races are the 
comparative lack of lustre, the ease with which the 
surface ridges can be made out with the naked eye, the 
facility with which they stain by the graphite method, 
the evenness of illumination when examined micro- 

Fig. 2>7- — Imbrication Lines on Lower Incisor oe aIalacotic 


scopically by reflected light (instead of a brilliant pencil 
of light from one point) ; and microscopically the 
"ridges" are seen to be both wider and deeper when 
examined by reflected light, and also in the ordinary 
way by sections. And it is a most significant fact that 
the more " susceptible " the mouth from which the teeth 
are taken, and the more malacotic in type the tooth is, 
the more marked and wider and deeper are the 


imbrication lines. This is well shown in Figs. 37 
and 38. Both photomicrographs are from the mesial, 
and therefore unworn, surfaces of lower incisor teeth. 
Fig- 37 shows the imbrication lines on a tooth removed 
from a young girl of eighteen with excessive dental 
caries. Fig. 38 shows the imbrication lines on a similar 
tooth from a woman of sixty, whose remaining teeth 
were quite sound, but were extracted for looseness. The 

Fig. 38. — Imbrication Lines on Lower Incisor of Sclerotic 


tooth in Fig. jy had succumbed to caries in ten years ; 
the othei (Fig. 38) had resisted for over fifty years. I 
do not state these facts as being absolutely cause and 
effect, but that they are related to a considerable extent 
seems indubitable. 

Only very occasionally do the outlines of the prisms 
show dark in unstained malacotic teeth. It is much 
more usual for the centre of the prisms to stain dark by 
the graphite method, as seen in Figs. 39 and 40. This 



means, of course, that the end of each prism is depressed, 
and in the hollow so formed the graphite has lodged. 

In some cases, by throwing a beam of light along the 
surface of the enamel, the centres of the prisms appear 
dark in a light hexagonal ling even when no graphite is 
used. This seems to show that the dark areas are 
depressions unilluminated. 

The average diameter of the prism ends stained with 



lie. 39. — Imbrication Lines and Depressed Prism Ends 


graphite is 0-00375 millimetre, and the average diameter 
of enamel prisms in this situation is 0-0057 millimetre 
(measured in sections by transmitted light). This 
should leave 0-002 millimetre as the thickness of the 
" unstained " rings, which is exactly what they do aver- 
age. These unstained margins of 0002 millimetre are 
too wide to be composed of cement substance only, and 
probably comprise the outer part of the enamel prism as 
well. Thus it would seem that in such cases the amelo- 


blasts have ceased functioning before the prisms were 
quite complete, and had left the centres — perhaps Tomes's 
processes — uncalciiied. I have only found such appear- 
ances in malacotic teeth. 

Sclerotic Teeth. 

So far only " native " and " malacotic " teeth have 
been contrasted. Sclerotic teeth of civilized races may 
be said, as far as histological appearances go, to fall 

- « 


Fig. 40. — The Same as Fig. 39, but More Highly Magnified. 

between these two classes, but much nearer the " native " 
in type than the " malacotic." Much more light is 
reflected from the surface of a sclerotic than from a 
malacotic tooth, but not so much as from a native tooth. 
The imbrication lines vary in their distinctness in 
different teeth of this class, but they are rarely so well 
marked as in the " malacotic " type. I have not 
observed any depression of prism ends in any sclerotic 


Pathological Fissures of the Enamel Surface. 

In addition to the increased development of the 
imbrication lines in malacotic teeth, there are three 
classes of fissures met with, and which I have classified 
as — (i) Calcarine, (2) Sinuous,. (3) Deep. 

The first kind apparently originate at the summit of 
the ridges, are broad, short, triangular in outline, and 
very numerous, and may be designated as " calcarine " 


Fig. 41. — "Calcarine" Fissures on the Surface or a 
Malacotic Molar. 

fissures. They are most marked on the mesial and distal 
surfaces, and on those points where the ridges are most 
marked — i.e., at a point one-half of the distance between 
the cervix and occlusal surface. Fig. 41 is an example 
of this class of fissure, stained, of course, by the graphite 

Fissures of the second class are not so numerous nor so 
frequently met with, are longer and thinner, and bear 
no relationship in origin to the ridges, many of which 


they cross. Fig. 42 illustrates these fissures, which 
might be termed " sinuous." on account of their thin 
wavy outlines. 

Both of these classes of fissures are best demonstrated 
by very light staining with graphite ; they are invisible 
without staining, and heavy staining obscures them. I 
have not seen them in other than malacotic teeth. 

The third class of fissure, classified above as " deep," 
run usually in the direction of the long axis of the tooth, 

Fig. 42. — Sinuous Fissures from a Lower Ixcisor. 

and vary considerably in length. They penetrate deeply 
through the enamel, and occasionally even into the 
substance of the dentine. Fig. 43 is an example of this 
kind of fissure stained with silver nitrate. That these 
latter fissures are not artifact is proved by the manner 
of preparation. The teeth were fixed in formalin 
immediately after extraction, washed and transferred 
without drying to a 10 per cent, solution of silver 
nitrate for twelve hours, washed again in running water 



for one hour, placed in the sunlight for one day, and then 
ground down slowly and examined frequently, so that 
the fissures could be traced from the surface inwards. 
Fig. 43 (an upper premolar) has been prepared in this 

This class of fissure is, of course, frequently seen in 
oidinary ground sections of enamel, but there is always 
the uncertainty as to their having developed during the 
process of grinding. As regards their origin, undoubt- 

Fig. 43. — " Deep " Fissures in an Upper Premolar. 

edly many are caused by traumatism, or possibly thermal 
changes ; but that some are developmental cannot be 
doubted, and may he due to the persistence of some 
portion of the enamel organ. 

Figs. 44 and 45 show such a cleft or fissure, stained 
with silver nitrate before cutting, and taken from the 
distal surface of a molar tooth. 

The enamel prisms on either side of the cleft are quite 
granular and indefinite in outline, and towards the 


Fig. 44. — Developmental Fissure in the Enamel near the 
Cervix of a Malacotic Molar (Low Power). 

Fig. 45.— The Same Section as Fig. 44, More Highly 

8S DENTAL caries and oral sepsis 

surface both they and the stratification striae show 
distinctly a certain amount of retroversion — as though 
there had been something retarding the outward 
movement of the enamel organ at this point. 

Opaque Spots. 

But little information has been gained from the 
examination by reflected light of " opaque spots " 
caused by initial caries, because of the technical diffi- 
culties of staining and lighting. Such areas do not 
appear to possess any definite structure, but are com- 
posed entirely of highly refracting globules when un- 
stained, and they take the graphite stain so deeply as 
to obscure all structure. When, however, calcarine 
fissures are present, caries can be seen attacking these in 
advance of the surrounding tissues. 


That these departures from the normal structure are 
potent factors in lessening the resistance of the teeth to 
caries cannot be doubted. They must favour considerably 
the adhesion of foodstuff and micro-organisms ; they 
expose a larger and more vulnerable surface to the action 
of the acid produced ; they negative both mechanical and 
physiological prophylactic measures ; and the fissures 
which have been described, since they allow of the pene- 
tration of silver nitrate and graphite, must permit the 
penetration of lactic acid, if not of carbohydrates. In 
fact, ceteris paribus, it may be quite logically inferred 
that the amount of graphite which an enamel surface 
retains is a measure of the amount of foodstuff it would 
tend to retain, and a demonstration of the situations of 
its retention. Added to which is the demonstrable fact 
that teeth so affected are not infrequently likewise the 
subject of caries. 

On the other hand, it may be thought, there is the 
common clinical experience as to hypoplastic teeth being 


by no means always subject to caries. Such teeth (non- 
carious) examined by the method I have indicated usually 
show the enamel surface to be free from any minute defects 
and having a very fair lustre ; even the surface ridges are 
frequently absent from the hypoplastic areas, because 
the striae of Retzius, or " incremental lines," run 
parallel to the surface, thus proving that the check to 
development occurred when the cap of enamel was only 
partly formed, and that normal enamel has been laid 
down afterwards, but that the rate of deposition at that 
particular spot has not increased sufficiently to restore 
the contour.* This is also borne out by sections of such 
teeth examined by transmitted light. The inference 
from this, of course, still further strengthens the 
relationship between minute structural defects and 
caries. The defects which are gross and obvious to the 
naked eye are not those which, as a rule, lessen the 
resistance of a surface to caries. 

* Such defects may be termed "healed hypoplasia." 



Permeability of the Enamel Surface. 

It is generally supposed that the surface of enamel is 
normally impermeable to fluids and stains ; in fact, 
Gabell and Austin* state that " it is quite impossible to 
stain enamel." This, however, cannot be accepted as 
an absolute fact. No doubt it is extremely difficult to 
stain healthy enamel with the ordinary stains, but a 
10 per cent, solution of silver nitrate will be found to 
stain the surface of all enamel, and, what is of more 
interest and importance, it stains to a varying degree 
in different teeth ; and not only does the intensity of 
the stain vary on the surface of the enamel, but it 
penetrates to a varying depth in different teeth. This 
having been ascertained whilst carrying out other ex- 
periments, the subject was investigated in the following 
manner : 

Perfectly sound teeth were placed in a 10 per cent, 
solution of silver nitrate for twenty-four hours, and then 
exposed to bright sunlight for a day. They were then 
washed in salt water, and sections cut in the usual way. 
The depth of penetration of the silver nitrate was 
measured by means of stage and eyepiece micrometers. 
Measurements were taken inwards from the enamel sur- 
face at intervals of i millimetre round the periphery of 
the enamel. The sum of these measurements divided 

* " Materia Medica for Dentists," p. 207. 


by the number of them gave the average for each tooth. 
In this manner it was found that the average penetra- 
tion for malacotic teeth was 0-27 millimetre (or 163 
micrometer divisions), and for sclerotic teeth 0-13 milli- 
metre (or 7-8 divisions) — that is to say, the stain pene- 
trated twice as far on the average in the malacotic as in 
the sclerotic teeth. 

The penetration is more regular in the latter variety, 
the maximum measurement being 0-25 millimetre. In 
malacotic teeth the stain tends to penetrate very deeply 
in places, whilst maintaining a general average penetra- 
tion greater than that of sclerotic teeth. The average 
maximum penetration in such teeth was 0*83 millimetre, 
or 50 divisions. These maxima penetrations are usually 
associated with some fissuring of the enamel. 

Maori teeth treated in a similar way invariably 
showed a less dense superficial staining, and the pene- 
tration was in some cases scarcely observable, the 
average penetration being only 0-07 millimetre, or 4-5 

In all varieties, wherever the enamel surface has been 
damaged by abrasion, fissures, or fracture, the stain 
penetrates more deeply than normally. Figs. 46 and 47 
illustrate the penetration of silver nitrate in malacotic 
and sclerotic teeth respectively. 

The degree of permeability of the enamel surface also 
bears an inverse ratio to the length of time a tooth has been 
erupted. This is illutrated by the following cases : 

1. Three teeth- — an unerupted lower third molar, an 
erupted upper third molar, and a lower premolar — all 
perfectly sound and from the same patient (aged twenty- 
two), were examined by this method, with the following 
result : 

Teeth. Amount of Penetration. 

Unerupted third molar . . 0*83 mm. (or 50 divisions). 

Erupted third molar (about two 0-42 ,, (or 25 ,, ). 

years' use) 
Premolar (half sclerotic type, 0-18 ,, (or 1 1 ,, ). 

eleven years' use) 



Fig. 46. — Photomicrograph showing Amount of Penetra- 
tion of Silver Nitrate in Malacotic Enamel, (f Obj., 
Xo. 2 Eyepiece.) 

Fig. 47. — Photomicrograph showing Amount of Penetra- 
tion of Silver Xitrate in a Maori Tooth. (| Obj., 
No. 2 Eyepiece.) 


2. The following teeth were taken from different indi- 
viduals : 

Teeth. Amount of Penetration. 

Unerupted third molar . . . . 0*50 mm. (30 divisions). 

Erupted third molar . . . . 0-30 ,, (20 ,, ). 

Molar from young adult . . 

• • 0-25 

.. (15 


Molar from old person . . 


„ (10 


The density of the stain in the last tooth was very 
much less than that in the third molars. 

3. The following teeth were taken from the skull of 
a Maori child aged about sixteen years : 


Amount o 

f Penetration. 

Unerupted third molar (incom- 

0*75 mm. 

(45 divisions). 


Erupting third molar (complete) 


(13 .. )• 

Second permanent molar (three 


(n-8 „ ). 

years' use) 

First permanent molar (nine 


(5 .. )• 

years' use) 

A point of importance to be noticed in the above 
groups is the comparative equality of penetration in the 
unerupted molars of both Maori and European. This 
would seem to point to the fact that the cause of the 
subsequent difference in the permeability of the various 
enamels is not entirely a developmental one. but rather 
is a property acquired largely after eruption. 

Comparing the second permanent molar of the Maori 
with the premolar of Group 1, it is seen that in two years 
the Maori tooth has become as impermeable as the 
European tooth has in eleven years. Such inferences 
do not, I am aware, agree with the accepted tenet that 
enamel once formed cannot possibly undergo any 
physiological alteration; but it is difficult to see what 
other logical conclusion can be drawn from the facts. 
especially when these are supported by others, as will 
subsequently be shown. 

The stain penetrates at first along the interprismatic 
substance, and then seems to spread laterally into the 
prisms. Fig. 48 is a photomicrograph of a transverse 



section of superficial enamel treated by the above 
method. It is seen that the interprismatic substance 
is stained darkly, but the prisms are not. In Fig. 49 
the stain is seen clearly running along between the 
prisms, without much invasion of the latter. 

Nature of the " Staining." 
It is perfectly obvious that all that is stained by the 
nitrate of silver is not organic matter, since the prisms 

I ig. 48.— Transverse Section of " Surface " Enamel, 
showing the interprismatic substance stained, but 
not the Prisms Themselves. 

themselves are stained; and I am not prepared to prove 
at present that any of the stained material is organic 
matter, though I think it is extremely likely that this 
will be found to be so. and for the following reasons : 
1. It is well kimwn that silver nitrate is a selective stain 
for the organic intercellular substance in other tissues. 


2. Hoppe-Seyler's analyses show a larger proportion 
of organic material in " infantile " enamel. 

3. The enamel of a malacotic tooth was heated in an 
electric furnace, so that the organic matter (if any) 
would be destroyed. It was then treated by the silver 
nitrate method, and the degree of penetration of the 
stain found to be very much lessened, being only 5 
divisions, or 0-08 millimetre. 

On the other hand, the staining may be a kind of ad- 

Fig. 49. — Vertical Section of Enamel, showing the Silver 
Nitrate penetrating inwards between the Prisms. 

sorption,* and the silver precipitated in microscopic in- 
terstices. This, however, for the present does not very 
much affect the argument. The fact remains that a 
fluid carrying a solid in solution can pass into the outer 
layers of enamel, and that the solid is there fixed either 

* The property of adsorption may be ascribed to some affinity 
between the molecules of the imbibing substance and that im- 
bibed. The retention of a gas or colouring matter by charcoal of 
water by the opal, or pepsin by fibrin, arc examples of such action. 


by chemical combination or by precipitation. The in- 
ternal enamel surface at the amelo-dentinal junction does 
not seem to be permeable, as is shown by the following 
experiment : 

The root of a malacotic tooth was sawn through, and 
the pulp cavity well opened. The tooth was then sealed 
in a small cup of wax, so that the crown projected into 
the cup and the root was below. The cup was then 
floated on silver nitrate solution in the dark. After 
exposure to the light, the enamel appeared a dark blue, 
but on cutting a section it was found that the stain had 
penetrated deeply up to the amelo-dentinal junction, 
but had nowhere crossed it. This was repeated with 
various modifications, but always with the same result. 
From this two inferences may be drawn : 

i. As was to be expected, no means of communica- 
tion exist between the enamel and dentine whereby fluid 
containing salts in solution or any other protective sub- 
stance might pass from the latter to the former. 

2. That that portion of enamel which is formed 
first is not permeable, but that portion which is last 
formed is permeable. 

The Density of Enamel. 

The word " density " is used here purposely, not in a 
common scientific sense, as being identical with specific 
gravity, but rather in the literal sense of "compactness." 
It has already been shown that some enamel (more espe- 
cially malacotic) is permeable to fluid to a certain degree, 
and that other enamel (sclerotic) is very much less per- 
meable. Now, in order to obtain a correct idea of the 
comparative " density " of two bodies which vary in 
permeability, it is obvious that some other method than 
weighing them in water must be adopted. The ordinary 
specific gravity method would, of course, give the correct 
specific gravity in each case, and it might be identical 
in each, but would not record the comparative " por- 


osity " compactness, or density with which the com- 
ponent parts were packed. For instance, spongy iron 
and ordinary iron have the same specific gravity when 
weighed in water, because water enters the porosities, 
and thus the specific gravity of the individual particles 
of iron is alone recorded ; but this is no gauge of what 
may be termed the " mass density " of the spongy iron. 

Precisely the same thing applies to enamel. For 
instance, suppose an individual and impermeable prism 
be separated out, and the specific gravity estimated. 
This would be precisely the same as that of the whole 
enamel were the prisms so tightly packed together that 
no fluid could enter. And suppose in the next case^that 
the prisms were loosely packed ; the fluid entering around 
them would again give the same specific gravity, but the 
mass density in the latter case would obviously be very 
much less than in the second instance. But suppose a 
fluid to be used which was incapable of penetrating 
between the prisms ; then a true record of the mass 
density would be obtained. 

The only fluid which can be relied upon for this pur- 
pose is mercury ; and since enamel floats in this fluid, it 
became necessary to calculate the density by means of 
estimating the weight of the volume of mercury displaced 
from a pycnometer by pieces of enamel of known weight. 
The density is then obtained according to the following 
equations : 

D= B ^c^, and B-(C-A)=E; 

Where A =weight of enamel in air. 

B=weight of bottle full of mercury. 
C=weight of bottle full of mercury and enamel. 
E =mercury expressed from pycnometer after in- 
serting enamel. 
(i3'6=specific gravity of mercury.) 

Enamel was obtained in the following manner : 
Sound teeth were placed in an electric furnace with a 
pyrometer attached, and heated to 300 C. for three 



minutes. On pressure being then applied to the crown 
of the tooth, the enamel separates from the dentine, 
sometimes as a complete cap, more often in pieces. In 
some cases pieces of the dentine adhere to the enamel. 
If this could not be readily separated, the whole piece 
was discarded. 

This is much the most practicable and accurate 
method of obtaining enamel free from dentine of which 
I am aware. The objection to it is that it might 
influence the result of the density. This may or may 
not be so, but is not at present of great importance, 
since the conditions were the same for all the teeth, 
and it is the comparative density which is being chiefly 
considered. I have cut sections of enamel so treated, 
and examined them very carefully under the microscope, 
and am unable to make out any change of structure 
at all. 

That a real difference does exist between the specific 
gravity and mass density of enamel is proved by the 
following test : The enamel of a sclerotic tooth was split 
off in the furnace (300 C. for three minutes), and divided 
into two portions. The specific gravity of the first 
portion, estimated by the water method — taking the pre- 
caution to boil the enamel and soak it in water for several 
hours after weighing in air, and before weighing in 
water — was 3-0 ; whilst the density of the second portion, 
estimated by the pycnometer and mercury method, was 
2-98 — that is to say, proportionately a smaller bulk of 
water was displaced than mercury. Or, expressed in 
another way. 3-0 represents the average specific gravity 
of the individual prisms, but 2-98 represents the density 
of the enamel as a whole plus enclosed air (most of the 
moisture or traces of organic material having been driven 
out wholly or partly by the previous heating). 

In all, sixty-four teeth were examined by this method. 
The number might perhaps have been more with ad- 
vantage, but it is extremely difficult to obtain a suffi- 
cient number of sound teeth of all classes. The process, 


moreover, to be undertaken with accuracy, involves a 
considerable expenditure of time. The temperature of 
the air near the pycnometer was taken regularly, and 
since it only varied slowly from 12 C. to 15 C., and 
since this would only affect the fourth decimal place, 
the results are not corrected for temperature. Through- 
out care was taken not to touch the pycnometer with 
the fingers, nor to allow the breath to influence its 

The following are the average densities of the enamel 
of the three classes of teeth examined by this method : 

Density of 


" Native " teeth . . . . 
" Sclerotic " teeth 
" Malacotic " teeth 




Thus it is seen that there is a maximum difference 
between the densities of " native " and malacotic teeth 
of 0-135 — a n °t inconsiderable amount. It will also be 
observed that there is nearly twice as much difference 
between malacotic and sclerotic teeth as between the 
latter and " native " teeth. The lowest density ob- 
served was 2-63, and the highest 3-06. The teeth were 
selected and classed empirically from a naked-eye ex- 
amination alone, and were otherwise selected indis- 
criminately as regards the sort of tooth — i.e., whether 
incisor or molar. 

The average difference between the density of the 
three classes of teeth may, perhaps, not be very great ; 
but having regard to the fact that the difference is 
probably due to the difference in porosity of the outer 
layers of enamel only, it would not be anticipated that 
the variation would be any greater. It is quite possible 
that some really sclerotic teeth were included amongst 

* Water = 1. 


the " malacotic." It is quite easy to be deceived in 
this matter by the naked eye, since one usually asso- 
ciates a darkened yellowish colour with a sclerotic tooth, 
and if it has not this colour it is apt to be classed as a 
malacotic ; whereas this by no means follows, some 
sclerotic teeth retaining their original lightness of 

It will be remembered that the permeability of enamel 
was found to decrease with the time after its formation. 
Therefore, if density is dependent upon this permea- 
bility (or porosity), we should expect to find a similar 
variation in density, though in the opposite direction. 
This, as a matter of fact, is found to be so. Teeth were 
taken from the jaws of a young Maori (about sixteen), 
and the density of the enamel estimated by the above 
method, with the following results : 

Tooth and Condition. 

Density of 


Third molar, unerupted, enamel incom- 
Third molar, unerupted, enamel complete 
Third molar, partially erupted 
Second molar, erupted, say, three years . . 
First molar, erupted, say. nine years 



0-02 5 

It is seen that the density is least in the incomplete 
and unerupted tooth, and greatest in the tooth which 
has been erupted for the longest time ; that the greatest 
increase in density occurs during the later stages of 
enamel formation ; that the least increase occurs during 
the eruptive stage. And seeing that the density of the 
enamel of the first molar is greater than that of the 
second molar, the logical inference is that the density 
goes on increasing after eruption. The only other ex- 
planation is that all the teeth had originally and per- 
manently different densities. This, however, I do not 
think at all probable, from my experience in examining 


the density of other Maori teeth. But the result of these 
estimations, taken in conjunction with the permeability 
experiments, make any such possibility even more 
remote. I think, therefore, as the result of these two 
investigations, that we may assume that the density of 
healthy enamel bears a direct ratio to the time which has 
elapsed since its formation. 

Hardness of the Enamel Surface. 

The methods which have been adopted in the past 
for the estimation of the comparative hardness of enamel 
do not seem to be of the right character. Resistance to 
crushing strain has been the principal scientific method 
used, but this, I think, does not meet the rase. It 
cannot be regarded as a measure of true " hardness." 
For instance, the diamond and carborundum are both 
harder than iron, but the latter will stand far more 
crushing stress than either of the former. 

The geological method of measuring hardness is far 
more exact and more applicable to the present case. 
In geology the hardness of minerals is measured by 
two methods : 

i. By scratching the surface with other minerals, 
thus placing them in a certain order, the one which is 
scratched by everything else being placed lowest, and 
the one which nothing else will scratch being placed 

2. By means of a special instrument — the " scle- 

The latter method seemed to offer the most exact 
method of recording the hardness of the surface of 
enamel, and it was therefore adopted. Fig. 50 shows 
the form of sclerometer which was used for the pur- 

It will be seen that the tooth to be examined is made 
to glide under a diamond point, which is attached to an 
accurately balanced brass rod. The rod beyond the 



point is graduated in centimetres and millimetres, and 
on the rod slides a 5 or 10 gramme weight. By altering 
the position of the weight on the rod, an increasing 
amount of pressure can be made on the diamond point ; 
and since the weight is known and the distance is known, 
it is a simple matter to calculate the actual pressure upon 
the point at any moment. The method adopted was to 
draw the tooth under the point with gradually in- 
creasing pressures until a scratch was made in the 
enamel which could be distinctly seen with the naked 

Fig. 50. — Diagram of the Form of Instrument used to 
indicate the variations in hardness of the enamel 

eye when rubbed with graphite. This method, of course, 
has its fallacies, in that it depends upon " what can be 
seen by the naked eye." This may vary with the ob- 
server and with the light. But in this case the observer 
was the same and the eyesight quite normal, and the 
light as far as possible always the same, in that all the 
observations were made before the same window and 
at the same time of day. 

The difficulties of the method, however, are far more 
serious than these fallacies. If a perfectly smooth sur- 


face could always be obtained the matter would be 
simpler ; but the varying curvature of the surfaces of 
the teeth, and the relatively marked or feeble develop- 
ment of the imbrication lines, make accurate observa- 
tion in many cases somewhat difficult. 

Another variation is introduced by the sharpness of 
the diamond point. Not that it wears or becomes smooth, 
but it may be accidentally broken, and the next point 
may not be of exactly the same shape or sharpness. So 
that only those teeth which are examined with the 
same point can be compared. 

The method is somewhat tedious, and only sixty-five 
teeth of various kinds were thus examined, but these 
results, I think, sufficiently indicate the comparative 
hardness of the various classes. The average weight 
required to scratch the enamel was as follows : 

Point No. i (very sharp). 

Sclerotic teeth . . . . . . 23*06 grammes. 

Malacotic teeth .. .. ..21*60 

Point No. 2 (blunt). 

Sclerotic teeth . . . . . . 1 50 grammes. 

Malacotic teeth . . . . . . 100 „ 

Point No. 3 (medium). 

Sclerotic teeth . . . . . . 33*0 grammes. 

Malacotic teeth . . . . . . 25*4 

I think there is no doubt that these results will be 
confirmed by further investigation by this method, and 
also by the method of scratching with different minerals. 
At present the indications seem to be fairly constant, 
and support our contention that there is a difference 
between " hard " and " soft " teeth ; that this difference 
is capable of being measured ; and that the terms 
" sclerotic " and " malacotic " in their literal meaning 
are justified. 


The Comparative Solubility of Enamel of Various Types. 

That all enamel is soluble in acid, provided the acid 
is sufficient in amount or acts for a sufficient length of 
time, has long been recognized, and also that some acids, 
strength for strength, have greater solvent powers than 
others. In this respect the researches of Head are very 
interesting. Head* has shown that the solubility of 
enamel in various strengths of acid varies in a very 
curious manner, and often that an acid of extreme weak- 
ness causes more destruction of the enamel than a strong 
solution of the same acid. For instance, he states that 
a i in 20,000 acid sodium phosphate solution causes 
obvious decalcification, whilst a I in 2,000 solution had 
no effect, and also that the total effect produced by the 
1 in 20,000 solution was greater than that produced by 
a 1 in 20 solution. Head, however, does not state the 
total amount of acid salt present in each solution, and 
this I regard as of much more importance than the 
degree of dilution, as will be seen by subsequent experi- 
ments ; neither does he state the type of tooth used in the 
various tests. Head also draws attention to the fact that 
whilst an acid of stated strength in watery solution 
produces decalcification, yet in a salivary solution it 
produces no effect. In this respect Head's work cannot 
be regarded as of much value, since apparently he did not 
estimate the total acidity (?) of the saliva after adding 
the acid. Obviously the acid in the saliva solution is 
largely, if not entirely, neutralized by the alkaline salts 
present, and also by combining with the proteid con- 
stituents of the saliva, and the surface of the enamel 
would be further protected by the insoluble precipitate 
of albuminate thus deposited. 

With a view to ascertaining whether enamel of various 
types differed in its solubility in similar acids of the 
same strengths, the following experiments were under- 
taken : . k =, 

* Dental Cosmos, 1907, p. 801. 


I. Qualitative Estimation of Solubility in Lactic Acid. 

The periods of immersion in the acid were short, the 
object being to compare the relative rapidity with which 
each variety of enamel was attacked. An indication of 
the amount of solution or partial solution which had 
taken place was obtained by scraping (or cutting) the 
surface of the enamel with a sharp scalpel, so that the 
softened enamel remained on the blade. The amounts 
of white powder appearing on the blade were compared, 
and recorded as + , ++,+ + +, the single + standing 
for a just perceptible amount of softening. 

1. Three malacotic teeth were suspended in lactic acid 
1 in 20,000 (0-05 c.c. in 1,000 c.c. distilled water). In 
twelve hours there was no observable effect ; in two days 
all showed dull surfaces, and a white film could be just 
scraped off with a sharp scalpel. At the end of three 
days an appreciable amount could be scraped off the 
surface of all the teeth, and under the microscope the 
surface showed disintegration. The decalcified film, 
however, could be removed from the surface of the 
enamel, leaving a " polished " surface* underneath. 

2. Malacotic, sclerotic (European), and Maori molars 
were placed in a similar solution (lactic acid 1 in 20,000). 
At the end of two days the surfaces of the malacotic and 
sclerotic teeth appeared dull, the Maori retaining its 
polish. With a sharp scalpel the surfaces of the mala- 
cotic and sclerotic enamel could be scraped very slightly, 
the former more than the latter, the Maori not at all. 
At the end of three days the malacotic and sclerotic 
teeth were quite dull to the naked eye, with a definitely 
formed film, and the Maori still retaining a polish. The 
enamel of all the teeth could be removed from the sur- 
face with the scalpel : the malacotic 4- + + , sclerotic 

+ + , and the Maori + . 

* This " polish " (under the microscope), however, is made up 
of innumerable scratches running in all directions, all true surface 
" structure 



3. Malacotic, sclerotic, and Maori canine teeth were 
placed in lactic acid of varying strengths, the same 
amount of acid being employed in each case. In this 
and the following experiments canine teeth were used 
exclusively, in order that the conditions might be as 
uniform as possible, and because these teeth are recog- 
nized clinically as being more resistant to caries. All 
the teeth were perfectly sound. The amount of solu- 
tion of enamel at the end of twelve hours may be tabu- 
lated thus : 

Variety of Tooth. 




Lactic Acid 

1 in 1000. 

0*05 c.c. in 50 c.c. 

Lactic Acid 

1 in 500. 

0*05 c.c. in 25 cc. 

Lactic Acid. 

1 in 100. 

0*05 c.c. in 5 c.c. 




+ + + 

+ + 

+ + + 
+ + 


+ + + 

+ + 


At the end of two days the relative amount of soften- 
ing in each of the varieties in each of the solutions was 
the same, though of course it had advanced a little in 
all. At the end of this time very little further softening 
took place — i.e., all the available acid had combined 
with the lime salts of the enamel. 

The amount of softening of the various enamels 
occurring in the three solutions A, B, and C, was most 
in C, less in B, and least in A, but the difference was not 
very marked — nothing like so marked, in fact, as the 
differences between the various enamels in each solution. 
(These results tend to show that the total amount of 
acid present is the important factor, and not so much 
its degree of dilution, the only difference being that in 
the extremely weak solutions a little longer time may 
be required. For instance, even with such an extremely 
weak solution as 0-05 c.c. in 1,000 c.c, the result was 


almost the same, at the end of three days, as that of the 
0-05 c.c. in 5 c.c. in one day.) 

In all cases surfaces which had been subject to attri- 
tion were attacked before unworn surfaces. But in the 
above records, since the malacotic teeth showed no 
attrition, only unworn surfaces are compared. 

II. Qualitative Solubility in Orange-Juice. 

Four crucial incisions were made in a Tahiti orange, 
and the following teeth inserted : Maori canine, sclerotic 
canine, malacotic canine (complete — i.e., having been 
in use for some years), malacotic canine (root incomplete). 
At the end of a week the teeth were removed and dried. 

The Maori Canine showed a questionable opacity in 
one small area, the remainder of the surface showing 
the normal lustre. 

The Sclerotic Canine was opaque and friable where a 
small fracture had occurred at the mesial incisive edge ; 
otherwise it was unaffected. 

The Malacotic Canine (complete) showed a slight 
opacity along the incisive edge, but the opacity was not 

The Malacotic Canine (incomplete) showed opacities 
down the centre of both lingual and labial surfaces, and 
also at the tip of the cusp. The opacities were all friable. 

The teeth were replaced in the same orange, but in 
fresh incisions, and examined at the end of the second 

The Maori Canine showed no increase of the original 
opacity, but a fresh and friable opacity had appeared 
on the edge of an attrition area ; otherwise the enamel 
surface was highly polished and hard. 

The Sclerotic Canine : The original opacity had be- 
come more friable, no further opacities had appeared, 
and the surface was otherwise normal. 

The Malacotic Canine (complete) : The original 
opacities along the incisive edge were more marked, 


and an opaque area had appeared on the mesial surface 
There was no loss of substance, and the opacities were 
not friable. 

The Malacotic Canine (incomplete) showed increased 
opacity of the original areas, and also loss of substances 
along the opaque line on the labial surface. 

The teeth were replaced, and examined at the end of 
the third week. 

The Maori Canine showed no fresh opacity, and, more- 
over, the original opacity seemed somewhat less marked. 

The Sclerotic Canine showed an increased friableness 
of the original area at the incisive edge, but was other- 
wise unaffected. 

The Malacotic Canine (complete) : The original opacities 
had increased in intensity and become friable at the cusp. 
Two fresh opaque lines had appeared on the lingual and 
labial surfaces. 

The Malacotic Canine (incomplete) : The whole of the 
enamel surface had lost its lustre, and the greater part 
of the lingual and labial surfaces were opaque. There 
was loss of substance on both these surfaces, and the 
cusp was very friable. 

III. Quantitative Estimation of Solubility in 
Hydrochloric Acid. 

Teeth of the following types were selected : Maori, 
sclerotic, malacotic, and malacotic unerupted. The 
whole of the teeth was covered with wax, and then 
two areas (each 4 mm. square) of the enamel surface 
of each tooth was exposed. Each tooth was then 
carefully weighed. They were then placed in 1 per 
cent, hydrochloric acid for forty-eight hours. At the 
end of this time they were removed, and washed in 
running water for twelve hours in order to remove the 
disintegrated enamel. They were then dried and 
weighed. Fourteen teeth were thus examined. They 
all, as would be expected from the action of such a 


powerful acid as hydrochloric, showed considerable loss 
in weight, but this loss again varied according to the 
" type " of tooth. The following are the average losses 
in the four classes : 

Class of Tooth. 

Loss of Weight. 




Malacotic (unerupted) 

. . 0-014 gramme, 
.. 0-018 
. . 0-028 
• • 0-050 

Thus it is seen that the unerupted malacotic teeth 
lost nearly twice as much as the erupted malacotic, and 
the latter lost half as much again as the sclerotic ; whilst 
the sclerotic lost one and two-sevenths as much as the 
Maori, and the malacotic enamel had lost exactly twice 
as much as the Maori. 

The results of these experiments on the solubility of 
enamel go to show that teeth do vary in their resistance 
to acids — to lactic, citric, and hydrochloric acids, at 
least. The results are remarkably uniform for all three 
acids, and show throughout that the enamel of malacotic 
teeth is most soluble, and that of the " native " teeth 
least soluble in all cases. Here, also, the empirical and 
clinical classification is justified by experimental in- 

The fact that the enamel of unerupted teeth was 
nearly twice as soluble as that of erupted teeth is very 
significant, and corresponds in this respect closely to 
the results of the " permeability " experiments. In fact, 
the results of these " solubility " experiments correspond 
so closely with those on the permeability of enamel that 
the inference cannot be avoided that the variations in 
solubility of the various classes of enamel is due to the 
variation in permeability. 

The Effect of Carbon Dioxide in Solution. 

It has been suggested that possibly the presence of an 
abnormal amount of carbon dioxide in the saliva might 
have a decalcifying effect upon the enamel. My ob~ 


servations do not support the suggestion. Analyses of 
saliva* give the total amount of carbon dioxide present 
as varying from about 40 to 60 volumes per cent. 
The greater part of this, however, is a chemical com- 
bination, and only a little over 3 volumes per cent, 
are in solution. A solution was therefore made up con- 
taining 60 volumes of carbon dioxide in 100 volumes 
of water (the actual amount being 1 litre). Maori, scle- 
rotic, and malacotic canine teeth (two of each) were 
placed in the solution for one month without the slightest 
effect being produced on any of them ; 2,000 c.c. 
of carbon dioxide were then dissolved under pres- 
sure in 500 c.c. of water, and a number of teeth kept in 
this solution for two months. At the end of this time 
neither softening nor opacity of the enamel had occurred. 
The only effect produced was that the calculus present on 
some of the teeth had become quite soft and crumbling. 

Hypothesis as to the Cause of Permeability and the 
Function of Nasmyth's Membrane. 

Sufficient evidence has, I think, been adduced to show 
that enamel is permeable, and that the permeability 
decreases in certain cases after the eruption of the teeth. 
It remains now to consider by what means this might 
possibly be brought about. It is obvious that when 
enamel is first secreted it must be in a semi-fluid 
condition, and that a subsequent hardening process 
must take place. This hardening or vitrifying process 
cannot be an extremely rapid one, and it seems that the 
evidence goes to show that this hardening process is not 
quite complete in the last-formed enamel when the tooth 
erupts. It is probable that the stellate reticulum has 
something to do with the abstraction of the lime solvent, 
and that it gets crowded out of existence, as it must do 
finally, before its function is quite complete. 

* Kulz, quoted by B. Moore, Schaffer's " Textbook of 
Physiology," p. 346 ; and by Halliburton, " Physiological 
Chemistry," p. 626. 


In considering the cause of the imbrication of the 
enamel surface, it was thought probable that an in- 
creased pressure on the ameloblasts in small jaws gave 
rise to the increased development of imbriae found on 
" malacotic " teeth. Subsequently it has been shown 
that the surface of malacotic teeth is also more per- 
meable, even at the time of eruption, than native teeth. 
The probability is that the two phenomena are due to 
the same cause — a too hasty completion of the enamel 
surface owing to pressure on the enamel organ caused 
by a too small crypt. 

The enamel after eruption of the tooth is covered by 
a dead membrane — Nasmyth's membrane ; it is im- 
mersed in a fluid, saliva, containing in solution lime salts 
and organic material (mucin and albumin), and it has 
been shown that fluid with solid in solution can pass 
into the outer layers of enamel. It would seem, there- 
fore, in every way highly probable that Nasmyth's 
membrane acts as an ordinary dialyzing membrane, 
through which crystalloids pass, but colloids do not. 
Therefore, other things being equal, and so long as the 
lime salts, especially the calcium phosphate, remained in 
solution, they must tend to pass through the membrane 
and penetrate the enamel, and the mucin and albumin 
are kept back. No doubt the process is very slow and 
gradual, depending largely upon the relative osmotic 
pressures on either side of the membrane, but it must 
undoubtedly take place. 

Now, the calcium phosphate is held in solution in the 
saliva by the presence of carbon dioxide, and this tends 
sooner or later to be given off. If it is given off early, 
then the phosphates are precipitated, and cannot, of 
course, pass through the membrane ; if it is not given 
off so soon, the phosphates will pass through the mem- 
brane in solution, but here sooner or later the C0 2 must 
be given off and pass back again, and the phosphates 
be precipitated. Now, if, as was shown to be probable, 
traces of the " enamel solvent " remain in the outer 


strata of enamel, this must be in a form of albumin, 
probably lymph charged with C0 2 ; but the C0 2 would 
be lost soon after eruption, and so the fluid come to 
consist of lymph alone. The phosphates therefore 
would be precipitated in an albuminous medium, and 
would form calcoglobulin, the peculiar indestructible 
nature of which is well known. Thus the minute inter- 
stices in the enamel would eventually be filled up and 
protected by a highly resistant substance. The rate at 
which this would take place is obviously dependent upon 
the condition of the saliva. If the saliva be scanty in 
amount, or if conditions are present which tend to pre- 
cipitate the phosphates and other lime salts, then the 
process will be retarded or entirely prevented. Simi- 
larly, an excess of viscid mucin in the saliva will be 
deleterious, since this substance is a non-electrolyte, 
and it is a well-known fact that the presence of non- 
electrolytes in solution with electrolyte salts consider- 
ably hinders, and may, indeed, entirely prevent, osmosis 
from taking place. This supports the clinical association 
between viscid saliva, malacotic teeth, and extensive 
caries often observed in children. 

Again, acids have a much lower " endosmotic equiva- 
lent " than alkaline salts ; and so, when enamel is first 
erupted and in a permeable condition, if lactic acid 
is formed on its surface, it will tend to pass through 
Nasmyth's membrane by osmosis at a greater rate than 
will the alkaline salts of the saliva, and thus give rise 
to that increased opacity of typical malacotic teeth 
which precedes their general destruction. It would also 
explain the considerably lessened effect of lactic acid 
on sclerotic teeth which have become less permeable ; 
since, owing to the occlusion of the porosities, no osmosis 
would be possible, and hence what solution did occur 
would be quite superficial, and therefore much slower. 

This hypothesis would explain, too, the staining of 
the enamel so constantly associated with sclerotic teeth. 
It is well known that such stains cannot be removed, 


and it is difficult to account for them unless it be by 
coloured fluids or salts of the saliva having passed into 
the outer strata of the enamel, and there becoming fixed. 
The further consideration of the subject is so inti- 
mately associated with variations in the composition of 
the saliva that it must be deferred until the latter has 
been dealt with. 

The Possibility of rehardening Enamel. 

Head* has recently stated that enamel, after partial 
decalcification (in acid calcium phosphate, weak lactic 
acid, and orange-juice), and subsequent prolonged im- 
mersion in saliva, not only loses the opacity due to the 
decalcification, but also becomes quite hard again. If 
this can be substantiated, and such hardening affected 
at will, it is obviously a most important matter, and 
one which might have very far-reaching effects in the 
treatment of initial caries. 

I have repeated Head's experiments, and carried out 
others on similar lines. Teeth — native, sclerotic, and 
malacotic — have been immersed in various strengths of 
lactic acid and of orange-juice, and exposed to the fermen- 
tation of carbohydrates with saliva, until well-marked 
opacities of the enamel were formed and the surface 
could be cut with a sharp scalpel. They were then 
transferred to saliva, and kept in it (with occasional 
changes of saliva) for a period of three months. The 
reaction of the saliva was always alkaline. At the end 
of this period the teeth were removed and washed in 
running water, dried carefully with filter-paper, avoid- 
ing friction, and exposed to the air for four hours. On 
examination, in one tooth- — a malacotic canine — the 
enamel, which was previously soft and friable, was 
certainly considerably harder, and the opacity had 
almost disappeared. In another tooth — a Maori canine 
— a very small and rather doubtful opacity had also 

* Dental Cosmos, January, 19 10, p. 46. 


disappeared. In all the remainder (seventeen) the 
opaqueness of the enamel was still present, and had not 
apparently decreased, although it seemed that in some 
cases the enamel had become slightly harder, and re- 
quired more pressure to cut it with the scalpel than it 
did originally. 

The results of these experiments, then, neither con- 
firm nor negative Dr. Head's theory. They will require 
repeating several times before a definite conclusion can 
be formed. I think it is not unlikely that it will be 
found that under certain conditions rehardening both 
can and does occur. The conditions may relate to the 
enamel, the manner and stage of its decalcification, or 
to the amount and character of the saliva. This requires 
very careful determination. 

There is one fallacy, however, which it is necessary to 
guard against. Very weak lactic acid produces an even 
opaque film all over the teeth immersed in it. This 
decalcified film may be removed, leaving a smooth, 
polished, and hard surface underneath. If, after being 
kept in saliva, in the process of drying this film be acci- 
dentally removed, it may be thought that the enamel 
had " rehardened." Such a mistake may be quite easily 
obviated by examination of the surface under the 
microscope. Partial decalcification up to the point of 
opacity does not destroy the imbrication lines nor the out- 
lines or central depressions of the enamel prisms. If, how- 
ever, the film of partial decalcification has been removed, 
all trace of normal structure has likewise disappeared. 

In the decalcification produced by the fermentation of 
carbohydrate, the opacity is of a different nature. The 
surface often remains highly glazed, but the acid pene- 
trates more deeply and irregularly into the enamel, and 
a rough, irregular surface remains behind after removal 
of the partially decalcified portion. So that it would 
seem to be indicated that, in further work on this 
subject, only enamel decalcified by exposure to lactic 
acid fermentation should be used. 



1. That the enamel of teeth varies appreciably as to 
surface structure, hardness, density, permeability, and 

2. That these variations are measurable, and in all 
cases bear a distinct relationship to the clinical classifi- 
cation of teeth into sclerotic and malacotic types — that, 
in fact, there is a demonstrable difference between 
" hard " and " soft " enamel, and that these differences 
are sufficiently constant to justify the terms. 

3. That this difference is not wholly developmental 
but is partly acquired. 

4. The difference in surface structure is, of course, 
wholly developmental. A nearer approach to the 
" native " type, and therefore a more highly resistant 
enamel, is to be attained by a more physiological use of 
the jaws in very early infant life, this continuing 
especially during the time that the roots of the deciduous 
molars are developing, in order to stimulate both the 
growth of the jaws and the full development of the 
tooth germ and crypt. 

5. The difference in density and permeability are 
probably partly acquired, and are dependent on the 
osmosis of lime salts from the saliva. The details of 
means whereby the saliva may be so modified or in- 
creased as to facilitate such osmosis are considered later. 

6. Finally, in order to obtain enamel of the highest 
resistance to caries, it is necessary to promote those 
conditions, hygienic, dietetic, and prophylactic, which 
will insure — 

(a) The normal development of the enamel organ to 
its fullest extent. 

(b) That the phosphates and other lime salts shall re- 
main in solution in the saliva for as long a time as possible. 

These conclusions are in the main largely supported 
by clinical experience. It has become somewhat un- 


fashionable of recent years to admit the accuracy of 
clinical experience when it stood alone. For instance, 
many older practitioners who have treated families for 
many years are of the opinion that teeth, if they are not 
destroyed by caries, do become " harder " after erup- 
tion ; but these opinions have been received with scepti- 
cism by the more modern school. But are we right in 
discarding such observations simply because they are 
not supported by the readings of a mechanical scientific 
instrument ? Are not the eyes, hands, and brains, of 
men long trained to their special work and fitted by 
years of observation, scientific instruments of extreme 
delicacv ? True, the personal equation is a factor to be 
reckoned with, but when the average of a large number 
of such observations is all in one direction we cannot 
do otherwise than accept the conclusions. 



It is not proposed here to deal with the minute analysis 
of enamel, but merely to give several facts which relate 
to its density and resistance. Von Bibra gives the per- 
centage of organic substances as 3-59 per cent., and the 
inorganic salts as 96-41 per cent. Hoppe-Seyler's 
analysis gave 3-6 per cent, organic matter. Tomes* 
was able to prove that enamel (elephant's) contained 
practically no organic matter, and that probably water 
of crystallization has been included under this head in 
previous analyses. 

No comparative analyses of human enamel from 
persons of different ages have been made, so far as I am 
aware, except that Hoppe-Seyler states that " infantile " 
enamel (enamel of unerupted teeth) contains more 
organic matter. This, however, is an important indica- 
tion, and will be referred to later. Recently an en- 
deavour has been made to show that those teeth which 
contained most organic matter were more resistant to 

In the Zeitschrift filr Physiologische Chemie for 1908, 
Band iv., p. 455, is published a paper by Gassmann, in 
which are recorded his results of the analysis of human 
and dog's teeth. The figures are given on the following 

The loss on incineration represents, of course, water 
of crystallization and organic matter. It will be seen 
from these figures, that apparently there is more or- 

* Journal of Physiology, 1896. 


ganic matter in human canine teeth and dog's teeth than 
in human wisdom-teeth. Yet, as Gassmann points out, 
the latter are more prone to caries, and this would seem 

Human Teeth. 



Milk- Third ^L°, f 
Teeth. Molar, Q P — 


Loss on Calcination 




% % 
3-76 6-91 8-17 
22-84 1 &'33 21-42 
29-59 31*65 30-25 



to infer that the more organic matter a tooth contained, 
the better the tooth would be. Herein lies a serious fallacy, 
for it does not appear that the author has taken into 
account the varying proportions of enamel in the various 
kinds of teeth analyzed. For instance, if a tooth had a 
large crown and a small root the percentage of lime salts 
would be high, and the organic matter relatively low, 
since the percentage of enamel would be high; and the 
converse would be true if the tooth had a small crown 
and a long root, where the proportion of enamel would 
be small. And it is just in these respects, unfortunately, 
that the two classes of teeth — canines and third molars 
— vary so greatly. 

Comparatively small amounts of tissue were analyzed, 
so that it cannot be claimed that an average was struck. 
Moreover, in the dog's teeth especially, if not in the 
others, wear and tear considerably diminishes the amount 
of enamel present, and thus the total percentage of lime 
salts in the tooth would be much diminished. And 
anyone who cuts sections of dog's teeth will be surprised 
at the comparatively small amount of enamel remaining 
in adult animals. 

It is not at all clear that an analysis of whole teeth can 
yield results of any value bearing upon the question of 


immunity and susceptibility to caries. The enamel alone 
is so essentially the tissue of resistance that the composi- 
tion of dentine and cement does not seem to enter into 
the question at all — at least, until it has been definitely 
proved that these latter substances vary in composition 
in direct proportion to the variation in the enamel of 
the same teeth. 

The Calcium Magnesium Balance. 

Rose* has shown by an extended series of investiga- 
tions that a relationship exists between the hardness of 
the water in any locality and the incidence of caries. 
He found that the condition of the teeth was related to 
the quantity of calcium salts in the drinking-water, but 
not to the quantity in farm products. He also states 
that the important factor is not so much the initial 
hardness as the stable hardness of the water — that is, 
the amounts of calcium and magnesium sulphates in 
solution which were not precipitated upon boiling. 

The most perfectly built teeth were found in provinces 
where the water, besides calcium, contained magnesium 
salts in the proportion of 4 : i. The character of the 
teeth, too, found in districts rich in mineral salts corre- 
spond to what we have described as sclerotic teeth, 
whilst those from districts poor in mineral salts were 
malacotic in type. 

The artificial addition of salts of calcium and mag- 
nesium to water has so far not been so successful as to 
warrant its adoption as a therapeutic measure, and Rose 
recommends the prescription of natural waters rich in 
mineral salts. He seems to ascribe the beneficial result 
of hard waters partly to more perfect development of 
the teeth, and partly to a resulting increase in the alka- 
line salts of the saliva. 

Now, Bunge has proved that when the intake of 

* Deutsche Monatsschrift f. Zahnheilkiinde, January-June, 


potassium salts exceeds that of sodium there is an 
increased excretion of sodium salts ; and Malcolm.* 
working by analog}', has shown that a similar relation- 
ship exists between calcium and magnesium. It has 
been shown that the ingestion of soluble magnesium 
salts causes a loss of calcium in adult animals, and 
hinders its deposition in young growing animals, while 
soluble calcium salts do not in the same way affect the 
excretion of magnesium. 

Weiske'sf experiments also support these findings. 
For instance, of two rabbits, one received i gramme 
CaCO a daily in addition to its food : the other i gramme 
of MgC0 3 for three months. The rabbits were then 
killed, and it was found that, although they were of 
equal body-weight, the total weight of the bones (dried 
and fat-free) in the first rabbit exceeded that of the 
second rabbit 77-45 grammes : 69-52 grammes) ; and, 
further, that the amount of organic matter in the bones 
of the MgCO :1 rabbit was in excess of that in the CaC0 3 

This would seem to be in opposition to Rose's view, 
that the addition of magnesium increased the resistance 
of the teeth to caries. Dr. Malcolm and the author 
therefore undertook an investigation to determine 
whether the ingestion of magnesium salts had a similarly 
deleterious effect upon the teeth. Four rabbits of the 
same age (six weeks) were selected : two were given 
ordinary food, and acted as controls : the other two were 
given in addition magnesium chloride in solution. The 
amount given was at first 1 c.c. of 0-25 per cent. MgCL, 
once daily. This was gradually increased up to 0-5 
gramme MgCL. At the end of three months the rabbits 
were killed. 

Macroscopicallv there was no difference observable 
between the teeth of the two sets of rabbits. Sections 
were made of the incisor and first molar teeth of each 

* / urnal f Physiology, February 28, 1905, p. 1 

f Quoted by Malcolm, loc. cit. 


rabbit. A microscopical examination of these revealed 
a number of minute differences, but nothing which could 
be regarded as constant or as distinctly abnormal. For 
instance, granularity of the enamel prisms and inter- 
globular spaces in the dentine were found to a slight 
extent in both series, but it could not be determined 
whether more in one than another. 

The density of equal portions of similar teeth was 
determined by the pycnometer and mercury method, 
the result being slightly in favour of the controls : 


MgCl 2 Rabbits 

Average density . . . . 1*924 


Difference =0*039. 

The hardness of the enamel of the incisor teeth, 
estimated with the sclerometer, showed the enamel of 
the " normal " rabbits to be slightly more resistant 
than the magnesium rabbits. Similar teeth were taken 
from the jaws of each rabbit and analyzed, with the 
following results : 

Weight of 
Dried Teeth. 

of Ash. 

of Organic 


of Calcium 

in Ash. 

Average for controls 
Average for MgClo rab- 
bits .. .. .. 





1 8-4 

The amount of difference is only slight. Evidently 
the teeth are not affected to the same extent as bones, 
though they are slightly and in a similar manner. Thus 
the magnesium salts evidently had the effect of lowering 
the percentage of inorganic and raising the percentage 
of organic material in the teeth ; also the average per- 
centage of calcium is a little lessened. 

Of course, whole teeth were analyzed here, too, though 
in this case, since similar teeth were taken, in each 


instance the relative amount of enamel was the same. 
There is no means of knowing, however, whether the 
differences existed proportionately more in the dentine 
than the enamel. 

The results, then, on the whole, of this investigation 
do not bear out Rose's views as to magnesium salts 
being particularly desirable for producing dense dental 
tissues. It would seem, perhaps, that the calcium salts 
are, after all, the more important. 

Rose's investigations are inconclusive in another 
respect, in that a large number of concomitant circum- 
stances as to habits and diet of the inhabitants of the 
various districts are not taken sufficiently into con- 
sideration, and may be such as to entirely negative any 
effect produced by the water. To quote only one in- 
stance : The geological formation of South Wales con- 
sists largely of calcareous and carboniferous rocks. The 
waters derived from these have a faintly alkaline reac- 
tion, and the mineral solids consist chiefly of sulphate 
and carbonate of calcium and magnesium.* Yet the 
incidence and extent of caries amongst the population 
is enormously high. 

On the other hand, the geological formation of the 
Scotch Highlands is largely granitic and Devonian. The 
water from such sources is often faintly acid in reaction, 
and contains only traces of lime and magnesia. f Yet 
the excellence of the Scotch Highlanders' teeth is pro- 

We conclude therefore that, although the hardness 
of the water may be a factor in the production of a 
relative immunity to caries, it is by no means so im- 
portant as to be an essential factor. 

* Parkes and Kenwood, " Hygiene and Public Health." 
| Ibid. 




For many years now it has been recognized that the quan- 
tity and composition of saliva has some effect upon the 
teeth. As to what exactly the effect is, however, there 
is a considerable divergence of opinion. So wide, in- 
deed, is the divergence that, whilst some observers 
ascribe immunity to caries to salivary protection, others 
ascribe the occurrence of caries to the deleterious effects 
of salivary constituents. 

It is perfectly obvious that a fluid in which the teeth 
are permanently bathed, which flows over the teeth to 
the possible extent of several pints daily, cannot be 
without effect upon the teeth. Again, since this is a 
normal physiological condition, it cannot be but that 
it is a beneficial one, and one which we should be 
justified in stating to be protective in function even 
though no more were known about it. Protection 
against disease is afforded to nearly all tissues largely 
by the fluid in which they are bathed, and the only 
fluid capable of so protecting the surface of the teeth is 
the saliva. It is, too, a general pathological law, and not 
confined to the human tissues, but pervading the whole 
of organized nature, that stagnation in any tissue or 
cavity makes for decay and disease, and favours the 
development of those general analytical forces repre- 
sented as a rule by the activity of micro-organisms ; 
and, conversely, all those forces which prevent stagnation 
and promote movement and circulation make for health 
and development. If the salivary secretion did naught 



else, it would be bound to act in such a manner by pro- 
moting a circulation in the mouth, and preventing oral 

Cases in which a diminution of the salivary flow ii 
so marked as to be noticeable, and perhaps distressing, 
are occasionally recorded, and these are almost invariably 
accompanied by acute and rapidly spreading caries of 
the teeth. Such cases are recorded by Miller,* Rigolet,f 
and Dubreuil-Chambardel. J 

Indeed, when we remember that the greater propor- 
tion of human beings exist on fermentable carbo- 
hydrates — and we have seen that even the teeth of 
races most immune to caries are attacked in vitro by 
the acids of fermentation — we recognize that there must 
exist some potent form of protection, or there would 
be no such thing as immunity to caries ; and, in fact, 
it is extremely likely that in the process of evolution 
teeth would long ago have succumbed. 

The importance of saliva in this respect — as the fluid 
which is largely responsible for the health of the buccal 
cavity and its contents — has not received the attention 
it merits. Attention has been so concentrated upon 
two of its components — ptyalin and mucin- — and their 
function in the digestion of starch and sw r allowing of 
food respectively, that nearly all else has been regarded 
as subsidiary. Pavlov, in his classical lectures on " The 
Work of the Digestive Glands," remarks that " the 
fluid must be of great importance as a cleansing agency," 
yet this is " hardly taken into account in physiology." § 
Even Pavlov, however, only thinks of the mucous mem- 
brane, and does not mention the teeth. 

Conditions of Normal Secretion. 

It is a most important fact to recognize, though one 
which appears to have been almost entirely overlooked 

* Dental Cosmos, 1903, p. 694. f Odontologie, April, 1901. 

X British Dental Journal, 1908, p. 880. 

§ "The Work of the Digestive Glands/' second edition, p. 69. 


by workers in the subject from a dental point of view, 
that the normal secretion of saliva is a reflex one ; that 
it is called forth in response to stimuli applied to various 
parts of the mouth ; and further, and most important 
of all, this reflex mechanism is, as we shall show, a most 
delicate one, but nevertheless a most certain and reliable 
one. It is one having far-reaching effects, and is capable 
of being either stimulated or depressed, and of bringing 
about very considerable differences in the composition of 
the saliva. 

The afferent side of the reflex arc is represented by 
the lingual and glosso-pharyngeal nerves in the tongue, 
and by their specialized terminations in the organs of 
taste, and also to a lesser extent by the sensory branches 
of the fifth nerve, supplying the buccal mucous mem- 
brane and teeth. It is the function of these nerves 
under normal conditions, upon being stimulated, besides 
making the act of mastication pleasant, to cause a 
secretion of saliva which is exactly adapted to the 
stimulus which called it forth. That is to say, the 
chief physiological use of the sense of taste is to control 
the activity of the salivary glands. It used to be 
thought that the excitation of the nerves of taste had 
a considerable effect on the gastric secretion ; but 
Pavlov,* in his work on these glands, has now come 
to the conclusion, and brings forth very convincing 
experimental evidence in support of the view, that the 
excitation of the sensory buccal and lingual nerves has 
no action whatever in directly stimulating gastric 

If this view be correct — and it appears to be sup- 
ported by Starling! — the association between the gusta- 
tory nerves and the salivary glands becomes all the 
closer. It becomes more clear that the raison d'etre 
of the nerves of taste is to act as sentinels in the mouth, 
on whose warning a flow of saliva appears, which com- 

* " The Work of the Digestive Glands," second edition, p. 91 . 
t " Recent Advances in the Physiology of Digestion." 


pletely envelops any substance in the mouth, neutral- 
izing and counteracting any harmful effects, and 
preparing the food for deglutition, or enabling it to be 
expectorated if disagreeable, in either case facilitating 
its rapid removal from the mouth, and preventing its 
adherence to the buccal tissues (including the teeth). Thus 
we may say that the function of the afferent buccal and 
lingual nerves is very largely protective, and their 
extreme importance, therefore, from a dental point of 
view — as being the originators of the means of automatic 
protection of the teeth — is at once evident. 

The efferent side of the arc is represented by the 
chorda tympani nerve to the submaxillary and sub- 
lingual glands, and by the auriculotemporal nerve to 
the parotid gland. Fibres of sympathetic nerves are 
also supplied to each gland, and these also transmit 
efferent impulses. 

The reflex path, then, is thus : The sensory nerves of 
the tongue are stimulated by some sapid substance ; 
the impulse passes up to the centre in the medulla, 
whence it is reflected down special fibres of the chorda 
tympani or auriculo-temporal nerve, and, arriving at 
the gland, causes an immediate secretion of saliva. 

It is upon the integrity, excitability, and " education." 
of this reflex arc that the protection and freedom from 
disease of the teeth very largely depends. 

Psychical Secretion. 

A copious flow of saliva of varying composition can 
be induced reflexly by means of stimuli conveyed via 
the optic, olfactory, or auditory nerves. This applies 
especially if the subject be hungry. That is to say. the 
sight or smell of certain articles of food, or the sound 
of its preparation (or even the dinner-gong), may cause, 
as is well known, the " mouth to water." 

The secretion may be modified considerably by other 
impressions, visual and mental, received at the same 


time, pleasurable stimuli increasing the secretion, and 
disagreeable sensations depressing the activity, of the 
glands. It is extremely doubtful, though, whether 
psychical secretion would occur if it were not for previous 
education of the gustatory nerves — i.e., certain sounds 
or sights having become reflexly associated by long 
experience with a pleasurable stimulation of the lingual 
and glosso-pharyngeal nerves. 

Sellheim* has performed experiments which show that 
after section of both of these nerves the secretion of 
parotid saliva in the day remained as copious as before 
when substances were placed in the mouth ; but it does 
not appear that the psychic effect has been eliminated, 
and that the secretion was not due to what might be 
termed a " memory reflex." 

The study of the salivary secretion has been until 
comparatively recently confined almost entirely to con- 
ditions when the efferent side of the arc was alone 
stimulated, the usual method of obtaining saliva for 
observation and analysis being by electrical stimulation 
of the chorda tympani nerve. This has at least two 
disadvantages : 

1. The stimulus is not a natural one ; it is in a form 
which is untranslatable, and we do not know to what 
it corresponds normally. 

2. It stimulates all the fibres in the nerve at one and 
the same time, and we have reason to believe that there 
are several different sets of fibres (or at least two), each 
having a specific effect upon salivary secretion, and 
excited by different reflex stimuli from the mouth. 

So that, having obtained a result by this method, we 
do not know under what conditions a similar result (as 
to quantity and composition of saliva) is obtained by 
the natural stimulation of the afferent buccal and 
lingual nerves. 

A similar objection may be made to the method of 
those who have worked at the subject from a dental 

* Quoted by Pavlov, ibid., p. 82. 



point of view alone, and have collected the saliva from 
the human subject during dental operations. The 
saliva so obtained cannot be relied upon as being in 
any degree normal, since the stimulus is essentiallv an 
abnormal, and perhaps a very painful, one, and a similar 
flow might be obtained, perhaps, by stimulating the 
sciatic nerve. Neither can chewing a piece of cotton- 
wool (as advocated by Miller) be regarded as being a 
natural means of exciting salivary secretion. The 
saliva so obtained does not represent any ordinary state 
of the oral secretions for that individual, since it is 
obtained under quite abnormal conditions. 

Sellheim* adopted the method of obtaining salivary 
secretion in the dog by means of food material and 
chemical substances placed in the mouth. There is, 
however, at least one serious objection to Sellheim's 
results from chemical substances — the latter were all 
used in too strong a solution to be comparable with 
ordinary dietetic effects. For instance, saccharine 
10 per cent, was used — a strength which would in the 
human being at least produce intense nausea. Even 
o-oi per cent, tastes very sweet indeed. The same 
objection applies to sodium carbonate 10 per cent, and 
sodium chloride 20 per cent. Similarly, hydrochloric 
acid 0-5 per cent., sulphuric acid 06 per cent., and 
formalin 0-5 per cent., are all far in excess of what 
could be normally tolerated. 

In fact, such results can only be taken as exemplifying 
the " rinsing " effect of saliva (so called by Pavlov) — 
the reflex secretion which occurs in order to rid the 
mouth of obnoxious or harmful substances (and is 
analogous to the reflex flow incited by certain dis- 
agreeable odours). It is a form of stimulation which 
under voluntary conditions occurs very rarely, and 
therefore the saliva so obtained must be regarded as 
being of very rare composition also. 

Again, too, an objection exists that salivary secretion 
* Quoted by Pavlov, ibid., p. 72. 


in the dog is produced under normal conditions by very 
different substances from human beings. A point which 
seems to have escaped observation in this connection 
is the shape, disposition, and function, of the teeth. 
A dog's teeth are not adapted for mastication of material 
like white bread, and he therefore spends much more 
time and muscular activity in eating a piece of bread 
than he would a piece of meat of similar size ; the bread 
bothers him, and is not natural. Whereas in the human 
being precisely the reverse obtains : the habit is to 
masticate meat carefully, because the teeth are flat- 
topped and not carnassial in type, and the tendency is 
to slightly squeeze food like bread between the teeth 
and to swallow it without proper mastication at all ; 
and lack of mastication means decreased salivary 

In order, then, to avoid these objections, the following 
conditions should be observed : 

1. The saliva should be obtained from the human 

2. It should be obtained by natural or ordinary 
methods of stimulation, or, if in the " resting stage," 
under known and constant conditions. 

3. The subject should be one in whom (in order to 
get " average " results) there is apparently an average 
salivary activity. 

In order that these conditions might be observed, the 
following series of investigations have been carried out. 
So far as I am aware, the effects of ordinary dietetic 
stimuli on the separate and combined salivary secretions 
in man have not been previously determined, the reason 
probably being the difficulty of collecting the saliva 
from the several glands during mastication. Langley* 
states : "In man the data are not sufficient to form an 
estimate of any value either of the relative amount of 
saliva secreted from the various glands or of the total 
amount secreted in twenty-four hours." The first 
* Schafer's "Textbook of Physiology," p. 491. 


thing then, obviously, was to devise an apparatus by 
which this might be done. For some time the diffi- 
culties were insuperable, but eventually the following 
means were adopted : For the parotid saliva a cannula 
was used in Stenson's duct. The ordinary cannulas or 
any small tubing obtainable were all either too large 
or made of too thick metal, so that the lumen, in pro- 
portion to the diameter of the cannula, was always too 
small. Cannulas were therefore made of thin German 
silver of as large a size as could possibly be inserted 
into the duct (the size being determined by first passing 
a graduated bougie, and marking the limit of its 
insertion). By bending the cannula slightly, it was found 
that it could be held in the duct* without much dis- 
comfort during the mastication of any substances. 

For the submaxillary and sublingual glands a small 
apparatus that might be termed a " segregator " was 
made. This is an appliance made of vulcanite, some- 
thing like an artificial denture, but having a hollow 
chamber attached at one side (made of soft vulcanized 
rubber). It is open at the bottom, and the margins 
are exactly applied to the floor of the mouth, so as to 
include the orifices of the submaxillary and sublingual 
glands. A metal tube (3 millimetres in diameter) has 
its orifice inside the chamber, and as nearly as possible 
over the opening of the ducts. The tube passes up 
through the vulcanite, through a space between the 
teeth, and then forwards in the buccal sulcus, where 
a small rubber tube is attached, which passes out of the 
mouth to the required receptacle. Fig. 51 represents 
the segregator diagrammatically. 

This apparatus was found to work well, and to give 
(within reasonable limits) very constant results. It does 
not, obviously, separate the sublingual from the sub- 
maxillary secretion, but these are probably very similar, 
so that it is not a matter of great importance. The 
saliva is secreted at considerable pressure, so that it 

* Securing it to the moustache was found to be a, good way. 



easily forces its way up the tube and round the bend ; 
no aspiration is necessary, and it is not desirable. 

The apparatus requires to be made, of course, from 
a plaster cast of the floor of the mouth of the subject 
of the observations. 

The investigation has been divided into several 
groups, according to the particular constituent of the 
saliva under observation. 

Having regard to the previous conclusion that prob- 

Fig. 51. — A, Upper Surface of Segregator ; B, Under 
Surface — Diagrammatic ; C, Diagrammatic Section of 
Segregator in Position. 

ably the chief function of the saliva is protective, it 
follows that probably, also, all its constituents are of 
importance from a protective point of view. I do 
not think it will be of any value to state here the com- 
position of saliva as ordinarily given in textbooks, since 
we do not know the exact conditions under which it was 
obtained. The chief constituents from a dental pro- 
tective aspect are — water, the alkaline salts of calcium 


and sodium, the phosphates of calcium and magnesium, 
ptyalin, sulphocyanate of potassium, sodium chloride, 
and mucin. 

Detailed observations have been made under varying 
conditions on all these constituents, and will shortly 
be described. In the first place, however, it is neces- 
sary to call attention to a most important point. 
The mere estimation of the amounts of constituents, or 
the " percentage composition." is of very little value by 
itself. It would be if the mouth were a sealed cavity, 
and always contained the same amount of saliva ; but 
it is not and does not. It is like a test-tube with a 
hole in the bottom, with a reagent flowing in at varying 
rates. Obviously, then, the other important thing to 
know is the rate of flow per minute, and to calculate 
the total amount of substance per minute present in the 

For instance, analysis may show 5 per cent, of a 
substance to be present ; but if only 1 c.c. of saliva 
flows per minute, it will not be anything like so effi- 
cacious, because there will not be so much of it. as if 
it contained only 2 per cent, but the flow were 5 c.c. 
per minute. 

It is the ratio, then, of the amount per c.c. to rate 
per minute which is all- important. In the subsequent 
estimations this total amount or value of any substance 
in the mouth per minute has been termed an " index " 
— i.e.. the " alkalinity index/' the " phosphatic index," 
the " ptyalin index." etc. 

It is evident, too, that the rate of flow must be 
extremely important in considering the mechanical 
cleansing of the mouth and teeth by the water of the 
saliva alone, and the dilution of the acids formed by 
fermentation. The greater the flow per minute, the more 
rapidlv will the acids be carried away. It is always a 
question of time. The organisms form a certain amount 
of acid from carbohydrate in a certain time, and it is a 
question whether the saliva can dissolve and carry away 


the carbohydrate debris or neutralize those acids as they 
are formed, or whether the acid production gets ahead of 
the saliva, and so is free to combine with the lime salts 
of the enamel. 

The Amount and Alkalinity. 

In the following estimations saliva was collected with 
the apparatus described, during the mastication of 
various substances used ordinarily as food. The 
amounts were measured to 0-05 c.c, and the alkalinity 
estimated by titration with - N y H 2 S0 4 , this extreme 
dilution being necessary to insure anything like accuracy. 
The titration was done immediately after collection. 
The indicator used was weak methyl orange. Other 
indicators are quite unsuitable ; litmus cannot be 
used, because it is affected by carbon dioxide, which 
is always present, and almost certainly in varying 
quantity and in varying conditions. If the saliva be 
boiled to drive it off, some of the alkaline salts are pre- 
cipitated, and this may interfere with the titration. 
Moreover, if acid phosphates happen to be present, 
these may turn the litmus either red or blue. 

Phenolphthalem also is affected by C0 2 , and cannot 
be used in the presence of ammonia, which is sometimes 
present in saliva, and it is therefore unsuitable. 

The alkalinity is expressed in c.c. of ^ H 2 S0 4 re- 
quired to bring the methyl orange to neutral point. It 
has been left as such on account of simplicity and the 
readiness with which differences may be recognized in 
reading a table of the results. 

The experiments were all done (with one or two 
exceptions) at the same time of day and under as 
similar conditions as possible as regards previous meals, 
exercise, occupation, and temperature of atmosphere. 
In the majority of cases the estimations have been 
repeated at least twice, and sometimes three times, 
where any uncertainty existed, and a number of early 


estimations of possible faulty technique have been 
discarded altogether. 

In order to have some basis of comparison between 
" resting " saliva — i.e., saliva present in the mouth some 
hours after eating — and saliva during mastication, the 
amount and alkalinity of specimens obtained by ex- 
pectoration was estimated on fifty consecutive days 
(excepting Saturdays and Sundays), two hours after a 
light midday meal, which always consisted of the same 
things. The average of these estimations is referred 
to as " normal resting " saliva. Fifteen minutes after 
collection of the saliva during mastication, the "rest- 
ing" saliva was also estimated, in order to gain an 
indication as to the possible prolonged effect of the 

Table I. gives the results of this series of estimations. 
It is seen that the amount of saliva per minute varies 
very much both from the parotid and from the sub- 
maxillary and sublingual glands ; that it may under 
some conditions from the parotid be ten times as much 
as from other stimuli ; that from the submaxillary it 
may be eight times as much from one stimulus as from 
another ; that the total amount of saliva per minute 
in the mouth likewise may vary in the same proportion 
— i.e., as 8 : i. 

A very noticeable point is the comparative smallness 
of the parotid secretion per minute. It never amounts 
to one-third of that from the submaxillary and sub- 
lingual glands, and may be as low as one-twentieth or 
one-thirtieth,* the average amounts being as i : 5-89 
for this series of stimulations. It seems not at all un- 
likely that this small quantity of parotid secretion is 
the most important factor in producing the increased 
susceptibility of upper teeth to caries (see p. 17). As 
regards the relationship of stimuli to amount per minute, 
it is quite obvious that the most sapid substances pro- 

* Smale and Colyer state that two-thirds are secreted by the 
parotid glands (" Diseases and Injuries of Teeth." p. 481). 


Substances masticated or used 
as Stimulant. 

Saliva duri * 


Submaxillary 1 

C.C. per 


linity per 

C.C. per 



Normal saliva (resting) to show 
increase or decrease 

Bread and butter (soft) 










Biscuit (soft) 








4'20 3 

Bread (dry) 

0- 3 





I '2 













" Brown " bread 







i-8o ( 

Grapes (very ripe) 



2-30 ( 





Carrot (boiled) 



2'00 ( 

Carrot (raw) 















Meat (mutton) 









Stewed apple 








* Two 



Resting Saliva Fifteen Minutes 
after Stimulation. 

Total S 

aliva from all Glands. 


C.C. per 


per C.C. 


per Minute : 



C.C. per 


per C.C. 






















1-03 2-90 





1-40 14-38 





o-86 2-84 

















0-84 6'90 





i-oo 1-80 





076 3-58 





075 3-60 



























































To face p. 136. 


duce the greatest flow, and of these sapid substances the 
ones which are most acid are the most powerful. 

The softest and least flavoured articles produce the 
smallest secretion. Compare the amounts from each 
of the glands and the total from all glands for the 
following substances : Buttered bread and orange, 
biscuit and apple, cake and celery, etc. Sweet sub- 
stances, like chocolate, dates, and figs, also produce 
a fair amount of secretion, but not so much as the acid 
ones. Pavlov found that dry substances in the dog 
produce the greatest parotid secretion. It is seen here, 
however, that, whilst dryness does increase parotid 
secretion in man (2 : 1) — cf. bread and butter (soft) and 
dry bread — it does not do so to anything like the same 
extent as acid substances, like soft stewed apple, for 
instance (1:6). All the substances except one produce 
an increase in the total amount over the resting saliva, 
in the case of acid substances very considerable, and 
of sweet substances very marked ; but in the case of 
the more tasteless articles the increase is very much less. 
Dry bread (white) doubles the amount ; brown bread 
(soft) only barely increases it by 0-15 c.c. per minute ; 
orange and apple increase it by more than six times. 
Bread and butter actually depresses the secretion by 
0-05 c.c. per minute. This, I think, is due to the de- 
mulcent effect of the butter. It prevents the oral 
mucous membrane from being stimulated, becomes 
fluid in the mouth, and possibly prevents any slight 
stimulus from the bread reaching the taste-buds, by 
coating the tongue or the particles of bread with an oily 
neutral fluid. 

The alkalinity of the saliva produced by the various 
stimulants shows similar, though not parallel, variations 
to the amount. The amount may be increased, but 
not the alkalinity per c.c. ; or the alkalinity per c.c. 
may be increased, but not the amount ; or both may be 
increased or decreased in varying proportions, according 
to the substance being masticated. The average 


alkalinity of the parotid saliva per c.c. is greater than 
that from the other glands ; but, owing to the lesser flow 
per minute from the former gland, the total alkalinity 
per minute is very much less. 

Here again is seen the fact that the most acid sub- 
stances produce the greatest alkalinity per c.c. Sweet 
substances markedly depress the alkalinity per c.c. (cf. 
chocolate, cake, grapes, banana, figs, and dates), but 
this deficiency may be in some cases more than made 
up for by the greater total quantity per minute. Al- 
though the variations in the alkalinity per c.c. are 
exceedingly interesting as showing the extreme delicacy 
of the mechanism controlling salivary secretion, and 
that a fluid exactly adapted to the stimulant is 
always forthcoming, yet it is the total alkalinity in 
the mouth per minute which is the most important 

Referring now to the column giving this (the first 
column of heavy figures) , it is made quite clear that 
acid substances produce an overwhelming alkalinity per 
minute as compared with such substances as bread, 
biscuit, cake, etc. — that, in fact, the alkalinity produced 
by acid substances may be to that produced by neutral 
ones as n : i. 

The question, though, naturally arises, Is the alka- 
linity so produced only sufficient to neutralize the 
acid substance in the mouth so that a mixture of the 
two would be just neutral ? From observations made 
on this point, it would appear that the saliva is 
always able to neutralize all substances (except in- 
tensely acid ones) during mastication ; but this point is 
not so important as the resulting reaction of the saliva 
and oral secretions some little time after the food 
material has been eaten — that is to say, does the 
stimulation or depression of the salivary glands cease 
with the swallowing of the stimulant, or is it con- 
tinued for some time afterwards ? Is there a sufficient 
" afterflow " to cleanse the mouth and neutralize and 


alkalinize any products of fermentation ? Obviously, 
from a prevention of caries point of view this is of prime 
importance. The columns in the various tables under 
"Resting Saliva Fifteen Minutes after Stimulation" 
provide the answers. 

It is apparent that the stimulation and depression 
is prolonged for at least fifteen minutes (and there is 
reason to believe for considerably longer). In only 
two instances is there an actual fall below the amount 
of " normal resting " saliva — in the case of bread and 
butter and boiled carrot. 

The alkalinity per c.c. shows a falling off in many 
instances- — bread and butter, bread (white and brown), 
cake, biscuit, and meat. The total alkalinity per 
minute — -the " alkalinity index "- — -is lowered also in 
several cases, chiefly by bread and butter, brown bread, 
meat, and biscuit. This, in view of the large proportion 
such articles form of our modern dietaries, is an ex- 
ceedingly important and significant fact. They are 
substances (except meat) from which, as we shall show, 
organisms are capable of forming a very large amount 
of acid by lactic fermentation in the mouth, and yet 
they are the ones which are least neutralized and diluted 
by the saliva. 

On the other hand, it is equally clear that, after other 
substances, the amount, the alkalinity per c.c, and the 
alkalinity per minute, are all markedly increased. 
Again, it is the acid substances which produce this 
effect (cf. orange, apple, pineapple, celery, carrot, 

The action of lemon requires some comment. During 
mastication, it evidently does not produce an amount 
of alkalinity equal to apple, for instance, although it is 
far more acid ; but two minutes after the cessation of 
the stimulus a profuse flow, with an exceedingly high 
alkaline index, occurs. This is to be accounted for, I 
think, by the stimulus in the first place being too strong, 
and producing a paralyzing effect upon the afferent 


nerves. * When the acid has been diluted and neutralized 
by the saliva somewhat, the full effect of the stimulus is 
felt, resulting in an alkalinity index three and a half times 
above normal. 

We are therefore justified in stating that the total 
amount of saliva poured out in response to acid articles 
of diet is more than enough to neutralize them, and 
is sufficient to exert a neutralizing and cleansing effect 
in the mouth for a considerable period afterwards. 

It would therefore appear from the above and subse- 
quent observations that it is extremely doubtful whether 
acid substances which have been masticated ever reach 
the gastric mucous membrane as acids. This, of course, 
does not apply to fluids, but even then, as is shown 
below (Table IV.. p. 146), the amount and alkalinity of 
saliva are increased to an extent which must make an 
acid reaction in the stomach of very short duration. It 
is therefore probable that when gastralgia follows the 
consumption of acid substances it is due to a salivary 

Variations in Secretion due to Taste Stimuli 

In the above series of estimations the substances have 
varied considerably in physical consistency, and have 
included practically only neutral sw T eet and acid flavours 
and their combinations. In order, therefore, to eliminate 
physical consistency, and to obtain results which should 
be due to the chemical nature alone, the following 
method was adopted : 

Ordinary plain biscuits were selected as a " base," and 
by soaking them in various solutions, and then re- 
drying them in an oven, the consistency remained the 

* This explains the phenomenon that people who suck lemons 
continuously — i.e., Sicilians — show a wasting of the enamel 
surface. Nevertheless, recovery of the salivary glands must take 
place similarly, for, despite the lessened resistance of the teeth, 
caries is very rare. 


same ; but each had its peculiar and distinctive 

The mere fact of adding water to the biscuits and 
then drying them produced a somewhat hardening 
effect, so that the control for this series must be a 
biscuit so treated, and not the normal untreated biscuit. 

Table II. shows the solutions and strengths in which 
they were used. The percentages of the solutions were 
such that they could be distinctly tasted, but not dis- 
agreeably so. The resulting effects on the amount and 
alkalinity of the saliva are tabulated as before. It is 
seen, firstly, that the mere fact of hardening the biscuit 
somewhat produces an increased flow and alkalinity 
from both glands, and also that the effect is prolonged. 

The pure sweet taste of saccharine produced an 
increase in amount, but not in alkalinity, per c.c. — in 
fact, this is slightly decreased — but the total alkalinity 
per minute is very considerably increased, and also lasts 
for some time 

Salt (sodium chloride) and quinine sulphate also act 
as salivary stimulants in no small degree, increasing 
both amount and alkalinity. But the falling off in 
the alkalinity of the subsequent " resting saliva " is 
very marked in the case of the sodium chloride ; 
probably, too, the amount falls considerably below the 
normal some time afterwards, for, as is well known, 
salt-flavoured articles produce an after " dryness of the 
mouth."* The prolonged action of the quinine sulphate 
is due, undoubtedly, to the fact that bitter flavours 
in the mouth are difficult to get rid of, and thus the 
afferent nerves are stimulated for a longer period than 
by others. 

Again, it is clear that an acid flavour — acid tartrate 
of potash — produces the greatest secretion and the 
highest alkalinity index, being nearly double that of the 
control during mastication. The increase is one of 

* The question of the relationship of the physiology of 
" thirst " to dental caries is at present under consideration. 



















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5-84 over the " normal " biscuit, and 373 over the 
" hardened." So that we may say that an increase of 
2-1 is due to hardening, and 37 to acidity. The com- 
bination of acid potassium tartrate and saccharine pro- 
duces a very similar effect, though not quite so marked. 
Oil of cloves, as representing aromatic substances, pro- 
duces very little increase in either amount or alkalinity. 
Its effect rapidly passes off, and, in fact, we get a sub- 
normal index at the end of fifteen minutes. 

Tannic acid, as might be anticipated, has a very 
inhibitory effect. The total amount during mastica- 
tion is i*2 ex., the alkalinity index 2*0 below the 
control, and the subsequent " resting saliva " is very 
markedly subnormal in all respects. This also is a very 
significant fact when it is remembered how prevalent 
is the habit of drinking stewed tea combined with 

Sodium carbonate, representing weal alkalies, also 
has a markedly depressant effect. The total amount per 
minute is 07 below the control, the alkalinity per c.c. 
is 0-35 below, and the alkalinity per minute is 1-98 
below, during mastication. Afterwards it apparently 
does not sink quite to normal, but this is not really 
so, since a little biscuit debris (of course strongly 
alkaline) was contained in the saliva tested. The 
mouth was not washed out to remove this, since the 
mere fact of doing so may alter the subsequent amount 
of saliva. 

The salivary glands are in some respects analogous 
to the pancreas, and Pavlov* has shown that the effect 
of alkaline salts upon the pancreatic secretion is in- 
hibitory. He has further observed that in a dog which 
had an oesophageal fistula, and had had an addition of 
soda to its food for several weeks, the food which fell 
from the fistula was " hardly at all insalivated "; 
whereas in dogs fed without the soda the food was 
always copiously insalivated. This depression by 
* " The Work of the Digestive Glands," p. 232. 



alkalies is another very important point, which will be 
referred to again subsequently. 

It has been shown, then, that acids are the stimulants 
which produce the greatest and most alkaline secretion 
of saliva. The question which next arises is, Are all 
acids alike in this respect ? 

In Table III. two inorganic acids are compared with 
two organic acids, the strengths of these solutions also 
being such as could be just comfortably tolerated. 


Substances masticated 

Saliva during Stimulation. 


and Sub 


Total of Sali\ 
all glanc 

a from 


or used as Stimulant. 

& 3 


>. . 







C.C. per 


per C.C 





Normal saliva (rest- 

ing), to show in- 

crease or decrease 




— . 

1-65 1-05 


Biscuit +H 9 S0 4 o- 1 

per cent. 








Biscuit + HC1 o-i 

per cent. 
Biscuit + citric acid 








7 per cent. 








Biscuit + tartaric 

acid 7 per cent. 





5 - 40 i'20 


It is seen that the tartaric and citric acids give both 
a greater secretion from all the glands and also a higher 
alkalinity per c.c, and therefore a much higher alkalinity 
index than the hydrochloric and sulphuric acids. Both 
the hydrochloric and sulphuric biscuits, however, pro- 
duced an astringent effect in the mouth, whilst the citric 
and tartaric produced a pleasurable sense of " succu- 



If these results, then, mean anything, they show that 
the afferent and efferent salivary mechanisms are 
indeed very delicate, and capable of appreciating very 
line differences in stimulation, such as the different 
flavours of the acids, and of being depressed bv some 
and increased by others. It is to be noted, too. that 
citric and tartaric acids ithe latter especially) are acids 
widely distributed in Nature in fruits and vegetables, 
and therefore in a form accessible and suited for 

The Effect of Liquids. 

Various liquids were drunk previously to eating a 
biscuit (normal and unhardened). to observe whether 
the amount and alkalinity of the saliva would be 
affected thereby. Table IV. gives the details of the 

It is seen that no increase — in fact, a decrease — is 
produced by plain water, both in amount and alkalinity. 
Tea likewise causes a decrease in the alkalinity, but 
increases the amount, probably on account of the thein 
acting as a vasomotor stimulant : the amount, though. 
is not equal to what it should be (see Table II.), and 
the alkalinity index is subnormal. 

Milk is only slightly better : ale produces a marked 
increase in amount and alkalinity, due to the alcohol 
and bitterness. The greatest increases, though, are 
produced by whisky and port wine. Whisky increases 
the amount, but the alkalinity per c.c. is decreased, 
also probably a vasomotor effect. Again, it is observed 
that the most acid liquid [i.e., port wine) has given rise 
to the highest alkalinity index. 

The effect of water, tea. and port wine on the resting 
saliva hfteen minutes after drinking is given below. 
The depressant effect of the tea on the alkalinity is 
again marked. 

Here, then, we have advanced a step farther, and see 



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that the character and amount of the saliva during the 
mastication of one and the same substance may be very 
materially modified by the fluids previously taken. 

Acid Dietaries. 

The above conclusion having been reached, we are 
very naturally led on to the next step, the consideration 
of the effect of an acid diet on the saliva. 

In order to determine this, an " acid " diet was sub- 
stituted for the ordinary diet for a period of eleven 
days. During the first six days nothing was taken 
either to drink or to eat (except small quantities of 
milk and bread) which had not an acid reaction. Chiefly, 
therefore, it was a diet of fruit and vegetables. Meat 
was taken, but was rendered acid by sauces. During 
the last five days other substances were also taken, such 
as bread and butter, potatoes, milk puddings, etc. ; but 
the meals always began and ended with " acids." The 
resting saliva was tested each day two hours after the 
midday lunch, and on eight of the days saliva was 
collected from the ducts during biscuit mastication. 

In Table V. and the chart (Fig. 52) the average results, 
without giving the details for each gland for each day, 
are shown. From a study of this table, it is at once 
evident that such a diet very materially increases both 
the amount and alkalinity of the saliva. The highest 
alkalinity index is during the second period for " rest- 
ing " saliva, but during the first period for biscuit 
mastication. (This discrepancy between " resting " 
and " stimulated " saliva has been noticed on several 

It is interesting to note how the amount per minute 
and the alkalinity per ex. increase gradually each day 
during each period. Between the sixth day and the 
seventh day of acid diet a day intervened on which 
ordinary diet was taken. The effect of this is evident 
in the marked falling off of the alkalinity index. It is 



noticeable, too, that during the period of mixed diet 
the amount per c.c. is greater than during full acid diet. 
This introduces other factors in salivary secretions, 
and ones which are still under consideration — the 
influence of the loss of water via the kidneys, bowel, 
and sweat glands ; for of course the acid salts of fruits 
are, in large doses, diuretic, aperient, and slightly dia- 


Salivary Secretion during an Acid Diet. 

Total Saliva from all Glands. 


Alkalinity Alkalinity 

per Minute. 

per C.C. 


Normal resting saliva, 

to show 





Average resting saliva 

for first 

six days 


i'i 1 


Average resting saliva 

for last 

live days 




Biscuit (previously) 




During full acid diet 

Day 4 












Partial acid diet : 

Day 7 




„ 8 








,, 10 




,, 1 1 




phoretic. It is interesting in this respect to note that 
between day 6 and 7 the alkaline salts of the saliva 
diminished, but the water increased during biscuit mas- 

There is obviously a most intimate relationship be- 
tween the salivary, renal, intestinal, and sweat glands. 
If the excretory glands are functioning to an abnormal 



extent, the salivary glands are either reflexly or directly 
sensitive to a diminished water-supply ; they secrete 
less, and thereby the mucous membrane of the tongue 
and mouth is rendered less moist. Thus, mechanically, 
an inducement to drink more fluids is brought about. 
the loss of water from the tissues is made good, and the 
salivary glands after a time resume their normal secre- 


Full /ic/ri Diet 

Partial Acid Diet. 





















. — 


1 1 


r\ — 


— • 




■ — 


Days I 23456780 '0 II 

Fig. 52. — Chart showing Increased Secretion and Alka- 
linity of Saliva to the Same Stimulus, i.e., Biscuit, 
during an Acid Dietary. 

a, Amount per minute ; b, alkalinity per minute ; c, alkalinity 

per c.c. 

tion. Here. then, we have another function of the 
salivary glands — to act as automatic indicators of the 
need for the intake of water. 

I think, therefore, that the increased amount of saliva 
per minute during the second period is due to decreased 
loss of water via the above channels. 

We have shown, then, how a feeble salivary stimu- 


lant may be converted into a strong one, and how 
an alkalinity index of 2-69 may be raised by dietetic 
means to one of 4-8 or 5-6, and that of " resting " saliva 
from 173 to 3-05. As a means of permanently raising 
the alkaline reaction of the mouth, neutralizing and 
diluting the acids formed by fermentation, and so pre- 
venting the occurrence of caries, this procedure must 
be so self-evident as to need no comment ; it is, moreover, 
eminently practicable. 

These results are in accordance with the observations 
of Haidenhain,* that the augmenting effect of a strong 
electrical stimulus extended over a period after its 
cessation, and that a weak stimulus applied after a 
strong one induced a greater secretion than a weak 
one did originally. 

Salivary Depressants. 

We now turn our attention to the other side of the 
question, and briefly consider those means by which 
the secretion and alkalinity of the saliva are depressed. 

It has already been shown that such substances as 
bread and butter, tea, tannic acid, sodium carbonate, 
and meat, actually depress the salivary secretion below 
normal ; and it is in accord with physiological principles 
to infer that the habitual consumption of such articles 
cannot but have a permanent effect upon the salivary 
glands in the direction of lessening their power for 
secretion. The general law that the frequent application 
of " overcomeable " stimuli is necessary for the de- 
velopment and full function of all organs must apply 
to the salivary glands also, and the constant absence 
of such stimuli must tend in the other direction, to 
lack of development or atrophy. (This will be de- 
monstrated subsequently by actual experimental 

There is a class of substances that have not yet been 

* Pfliiger's Archiv, xvii., 1878. 


referred to, but which must act in this direction, that 
are not articles oi diet, but of which enormous quantities 
in the aggregate are used by the public. I refer to 
tooth po-ii'ders and pastes. Practically the universal 
base for these dentifrices is calcium carbonate, com- 
bined with other alkalies, such as sodium and magnesium 
carbonates and soap ; a minute quantity of antiseptic and 
some aromatic flavouring agent are also usually included. 
They are used to " neutralize the acids of the mouth." In 
other words, they are used to do what it is presumed 
Nature cannot do : they are, as it were, a crutch for 

Total Saliva Five Minutes after the Use of Dentifrices. 

Substances used as Dentrifrice. 

C.C. per 


per C.C. 




Normal saliva (resting), to show in- 

crease or decrease 




Chalk, soap, and carbonate of 

soda, with tooth-brush 




The same used with finger, traces 

remaining in mouth 




Chalk, carbonate of soda, cloves, 

and gaultheria 




Acid potassium tartrate (powder) 




poor, feeble Nature to lean upon. It is as if one 
should in all cases of dyspepsia, irrespective of its cause, 
give constantly and continuously an artificial gastric 
juice, or, in the case of an enfeebled heart, insist on 
a patient maintaining the recumbent position until 
the heart became as strong as normal. 

The action of such dentifrices on the salivary secretion 
is shown in Table VI. It is seen that a simple dentifrice 
without flavouring agents very considerably reduces 
the alkalinity and the amount of the saliva ; that even 
when some of the powder remained in the mouth, the 


total alkalinity of the mouth five minutes afterwards was 

The addition of flavouring agents decreases the de- 
pression to a slight extent, but the resulting oral re- 
action is still markedly below normal. Similar tests 
have been made on a number of individuals, and 
always with the same result — a marked lowering of the 
alkalinity index. Comparing these results with that 
after the use of acid potassium tartrate as a tooth- 
powder, we see that the latter produced a consider- 
able rise in amount per minute and alkalinity per 
c.c, and that the total alkaline reaction of the mouth 
five minutes afterwards is raised from an index of 173 
to 2-28. 

We cannot but conclude from this that the use of 
alkaline dentifrices for the prevention of caries is 
wrong, is physiologically incorrect, unscientific, and 
empirical ; and not only so, but also actually con- 
ducive to the inception and progress of disease, by 
decreasing the circulation and alkalinity of fluids in 
the mouth. 

The use of alkalies seems to be based upon a wrong 
conception. It is as though it were thought that lactic 
acid developed and accumulated in the mouth, remain- 
ing there for some hours or until next morning, when an 
overwhelminglv strong alkali is introduced to neutralize 
it ; whereas, of course, as each molecule of lactic acid 
is formed, it searches for something wherewith to com- 
bine. Alkaline salts of the saliva will obviously most 
readily satisfy it. but should these not be available, then 
the calcium phosphates and carbonates of the enamel 
surface are utilized. 

It cannot be too clearly recognized that, by the 
use of alkalies, only those molecules of acid formed 
immediately previously can be neutralized, and also 
that the natural defensive forces of the mouth are 
thereby lowered for some considerable time after- 


Diminished Taste Perception. 

It would seem not to be wrong to infer that the 
habitual consumption of substances which fail to 
stimulate the endings of the lingual and glosso- 
pharyngeal nerves in the tongue, especially during the 
years of development, would lead to their becoming 
excitable or dulled in their appreciation of the different 

ste stimuli. 'There are substances, too, such as 
alcohol and tobacco in excess, which, as is well known, 
interfere with the sense of taste.) 

Assuming, then, for the present that this does take 
place, the following experiments were done to determine 
what the effect would be on salivary secretion. The 
condition of dulled taste appreciation was artificially 
produced by painting various parts of the tongue with 
cocaine. This at first, of course, produced a profuse flow, 
owing to its bitter taste : but this rapidly passed off, 
and after ten minutes the saliva was collected during 
mastication and observed. Table VII. shows the 
results. When the anterior two-thirds of the tongue is 
cocainized, there is an obvious diminution of both total 
amount and alkalinity [cf. Table II.). 

Cocainizing the posterior third of the tongue produces 
even a greater diminution in both amount and alkalinity 
of the total saliva during biscuit mastication, the de- 
ssion being chiefly in the amounts per minute from 
each gland. During apple mastication the dec: - 
from the normal [cf. Table I. is very considerable from 
all the glands in both amount and alkalinity, the total 
alkalinity per minute being reduced by 70 per cent. 

The results of partially cocainizing the whole tongue 
are very much the same as in the latter case, the dec s 
in amounts per minute being more affected than the 
alkalinity per c.c. ; but the alkalinity index is even more 
reduced than by cocainizing the posterior third alone. 

That similar states may be present abnormally in the 













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mouth seems to be extremely probable. I have esti- 
mated accurately by titration the perception of such 
tastes as sweet, bitter, and acid, in about a dozen in- 
dividuals ; and although this number is insufficient from 
which to form definite conclusions, it is sufficient to 
show that the sensitiveness of the nerve endings of the 
tongue does vary perceptibly in different individuals, 
and, moreover, that a dulled taste sensibility and marked 
susceptibility to caries seem to be associated. 

Salivary depression may be induced psychically. 
Pavlov* has observed that strong excitement in a dog 
may be sufficient to entirely suppress the flow of saliva. 
The same thing is well known to occur in the human 
subject. The effect of strong mental concentration is 
always to produce a condition of " dry mouth "; the 
urinary secretion is stimulated, but the salivary secretion 
is depressed. 

On the other hand, strong muscular exertion produces 
at first a much increased flow of saliva, followed some 
time afterward by a diminution and a sense of dryness, 
due, most probably, to loss of water from the body via 
the sweat glands. 

Here, then, we find two concomitant conditions of 
higher civilization — i.e., increased mental excitement 
and subnormal muscular exercise, both tending in the 
direction of decreased salivary secretion. 

It has frequently been noted that climatic changes— 
a rapid change, for instance, from the Temperate to the 
Torrid Zone — is followed by a rapid increase in the pro- 
gress of dental caries. This may be due, to a certain 
extent, to a change in diet, but is more likely to be due, 
I think, to the disturbance of the established balance 
between the kidneys, sweat, and salivary glands, acting 
in nearly all cases in an excitation of the two former 
and a depression of the latter. This is the more probable, 
since Englishmen at least, as is well known, wherever 
they may be, insist as far as possible upon an " English " 
* hoc. cit., p. 86. 


dietary, instead of adapting themselves to that dietary 
which the process of evolution has demonstrated to be 
the most fitted for each particular locality. 

Experimental Evidence from Lower Animals. 

A series of experiments has been carried out in 
rabbits to determine the possible effect on the salivary 
glands of decreased stimulation of the gustatory nerves. 
Rabbits were chosen for the purpose, since in them the 
salivary glands must be of great necessity, as they do 
not drink. 

I. The effect of softened and partially neutralized 

(a) Two rabbits of equal age (two months) were 
selected. A was fed on cabbages, turnips, carrots, and 
grass, previously boiled in weak sodium carbonate 
solution ; B was fed on the same food, but unboiled and 
in the natural condition. At the commencement of the 
experiment A weighed 617 grammes, and B weighed 
602 grammes. The experiment continued for a little 
over four months (nineteen weeks). At the end of this 
time A weighed 1.275 grammes, and B weighed 1,077 
grammes. The animals were killed, and the sub- 
maxillary glands removed and weighed. The mean 
weight of the submaxillary glands of A was 0-4250 
gramme ; the mean weight of the submaxillary glands 
of B was 04325 gramme. Thus it is seen that, although 
A was 200 grammes heavier than B. it had the smaller 
salivary glands. Expressing these as weights per kilo- 
gramme of body-weight, we have A = 03336 gramme. 
B = 0-4004 gramme, a slight difference, it is true, but 
still quite appreciable, especially considering the com- 
parative shortness of the time (nineteen weeks). The 
submaxillary glands only were examined, since in the 
rabbit the parotid gland is said to secrete continuously, 
irrespective of stimulation. 

(b) An exactly similar experiment was commenced 


with two other rabbits, very much younger, two to three 
weeks old. in order to avoid the initial " education " of 
the gustatory nerves, and the subsequent possible 
" memory reflex secretion." C was fed on boiled 
neutralized food, and weighed at the commencement 
285 grammes. D was fed on similar food, untreated, 
and weighed at the commencement 259 grammes. Un- 
fortunately, at the end of a fortnight D was killed by 
another rabbit ; C afterwards developed most marked 
rickets in all its long bones, and the front-feet became 
completely retroverted. At the end of three months 
(twelve weeks) it was killed. At the time of death C 
weighed 485 grammes, and the mean weight of the sub- 
maxillary glands was 0-2125 gramme. D, when it was 
accidentally killed, weighed 270 grammes, and the mean 
weight of the submaxillary glands was 0-2362 gramme. 

If these may be compared, then it is seen that, although 
C was four times the age and nearly twice the weight of 
D, yet its salivary glands were very appreciably less in 

2. The artificial elimination of the gustatory sitmuli. 
Rabbits were anaesthetized (with chloroform), and 
various portions of the mucous membrane and subjacent 
tissue of one side of the tongue were removed with the 
electric cautery. After the lapse of a few months the 
weight of the glands on either side was compared. The 
left side of the tongue was always selected, since Bidder 
and Haidenhain* found that in the dog at least the left 
submaxillary glands are as a rule larger than the 

(a) A full-grown wild rabbit (weight 1,140 grammes) 
was anaesthetized, and the whole of the mucous mem- 
brane and submucous tissue of the left side of the tongue 
was removed with the electric cautery. The rabbit 
made a good recovery, and was fed on ordinary fresh 
food for a period of two months. It was then killed. 

* Quoted by J. N. Langley in Schafer's " Textbook of 
Physiology," p. 487. 

i 5 8 


and the glands removed and weighed, with results as 
shown in the following table : 

Weight of Right Gland. 

Weight of Left Gland. 

Weight of Rabhit. 

0*558 gramme 


0*4300 gramme 

1,160 grammes. 

expressed as per 
kilo of body- 

Thus it is seen that at the end of two months the gland 
receiving its stimulus from the side of the lesion was 
appreciably less in weight than that on the normal side, 
the diminution being one of 0-1017 gramme per kilo of 
body- weight. 

(b) Another full-grown wild rabbit, weighing 1,299 
grammes, had the mucous membrane removed from the 
anterior two-thirds of the left side of the tongue in a 
similar manner. It was fed on precisely similar food to 
the other rabbit, and was kept for the same length of 
time (two months). The following were then the 
weights of the glands : 

Weight of Right Gland. 

Weight of Left Gland. 

Weight of Rabbit. 

0*5210 gramme 


0*4762 gramme 

1,270 grammes. 

expressed as per 
kilo of body- 

Here again is a distinct difference between the two 
glands, the diminution in this case amounting to 0-0441 
gramme per kilo of body-weight, or a little less than 
half the diminution observed when the whole of the 
mucous membrane was removed. If any inference 
could be drawn from this, it would be that the stimula- 


tion arising from the excitation of the glossopharyngeal 
nerve is of somewhat greater importance than that from 
the lingual nerve. 

(c) A full-grown tame rabbit was also the subject of 
an exactly similar experiment to the last. The opera- 
tion, however, seemed too severe for it. A curious form 
of toxaemia was set up, and the animal died with con- 
vulsions in one week. Although, therefore, the experi- 
ment may be said to have failed, it is interesting to note 
that in this case also the gland on the side of the opera- 
tion was 0*059 gramme less than the other. 

In all the above experiments the animals were killed 
in the fasting state, when the glands should be at their 
largest.* In all the tongue experiments the operation 
caused immediately great salivation and very marked 
swelling of the submaxillary gland of that side. The 
increase in the size of the gland was both palpable and 
obvious. On the third day, however, the salivation and 
swelling disappeared almost suddenly. 

In these experiments, although the differences in the 
weights of the glands are not great, yet they are fairly 
constant, and, moreover, one has to remember (1) the 
comparatively short duration of the loss of excitation ; 
(2) the effect of the psychical stimulation, and this 
would probably be increased by the fact of one side of 
the tongue being normal ; (3) the fact of the animals 
being full-grown. 

An endeavour has been made to eliminate the age and 
psychical factors by selecting quite young animals, but 
up to the present the experiments have failed. 

Efforts were made to estimate the amount and 
character of salivary secretion in the above series of 
rabbits during life, by collecting the saliva by aspiration 
from the mouth after the injection of pilocarpine 
(1 milligramme per kilo of body- weight). Although 
this method cannot be relied upon for anything like 
absolute accuracy, yet it may be noted that on three 
* J. N. Langley in Schafer's "Textbook of Physiology," p. 487. 


out of four occasions the rabbit fed on boiled neutralized 
food yielded from one-half to one-third less saliva per 
minute than the normal rabbit, and also the percentage 
of alkaline salts and total alkalinity per minute were 
correspondingly diminished. With regard to the wild 
rabbits, the element of fright was so predominant as to 
make the results too variable to be of any value. 

It may be concluded therefore that in animals a diminu- 
tion in the excitation of the gustatory nerves leads to a loss 
eight in the salivary glands, and presumably also to 
a corresponding loss of function. 


The fact that ptyalin may act as a protective agent 
for the teeth seems to have been overlooked, though on 
consideration it would appear to be quite clear that this 
is so. The function of ptyalin is to convert starch into 
sugar; and although Cannon* has recently shown that 
the salivary digestion of starch may go on in the stomach 
for some time after its being swallowed, yet there is no 
doubt that the amount of starch so converted is. in 
proportion to the total amount eaten, extremely small. 

The saliva of many animals contains no ptyalin.. 
notably in the carnivora. including the dog. yet the 
latter digests starches very completely ; the saliva of 
the horse, too. I have ascertained, possesses extremely 
feeble diastatic properties, yet it exists very largely on 

If, then, the salivary digestion of starch in the stomach 
is of but little importance, why is ptyalin present in 
saliva ? There can be but one reason — in order to 
digest starch debris in the mouth. In other words, to 
convert a solid insoluble and adhesive substance like 
starch into a very soluble and easily removable sub- 
stance, such as is maltose, to prevent stagnation and 
promote circulation. 

* American Journal of Physiology, 1904. 


Now, since maltose is probably more easily fermented 
by the mouth organisms alone than is starch, it will 
obviously be of advantage either to have no ptyalin at 
all present or to have a considerable amount, so that 
the organisms either should not be aided in their work 
or that their pabulum should be rapidly swept away. 
Moreover, the conversion from starch to maltose is not 
a simple process ; erythro-dextrin and achroo-dextrin 
are intermediate products. Now, the sticky, adhesive 
nature of dextrin is well known ; and if the ptyalin be 
small in amount the conversion process will be a corre- 
spondingly slow one, and the dextrin formed will remain 
longer, and so tend to bind the substance closer and more 
firmly to the teeth. Again, free organic acids destroy 
the diastatic action of ptyalin ; if, then, when the 
starch is slowly and partially converted into maltose 
and dextrin, the organisms incorporated in the mass 
form free lactic acid, no further action of the ptyalin 
takes place, and the starch is literally gummed to the 
teeth, to be slowly but surely transformed into lactic 
and other acids. 

On the other hand, if the action of the ptyalin is much 
more rapid than that of the organisms, there will be a 
fair chance of all the starch being converted into mal- 
tose, and so carried away, provided there is adequate 
salivary secretion. Now, although in the case of 
ferments the actual amount of substance eventually 
converted does not depend upon the amount of ferment 
present, yet the rapidity of that action, especially in the 
initial stages, does depend upon the amount and its 
concentration. It is therefore of advantage to have as 
large an amount of ptyalin per minute present in the 
mouth as possible. 

The ratios of these amounts, in salivas produced by 
a series of dietetic stimulants, have been determined. 
The method used was that of Mett's tubes. Fine glass 
tubing — not quite capillary — is filled with starch 
coloured blue with iodine. The tubing is then divided 


into short lengths of about I cm. and placed in the 
sample of saliva to be tested. (The tubes are kept 
horizontal, and the capsules covered to prevent evapora- 
tion.) The saliva is then incubated for one hour at 
36 C, and the amount of starch converted — i.e., 
amount of disappearance of blue coloration from each 
end of the tube — is read off under the microscope by 
means of an eyepiece micrometer and very low power 
objective. The method gives very constant results. 
The amount of ptyalin, however, is not directly pro- 
portional to the measurement so obtained. Schutz 
and Borisov have formulated a law, endorsed by 
Pavlov,* that a ferment in a fluid varies with the square 
of the length of the column of digested starch measured 
in millimetres. This law has been in the present in- 
stance applied to saliva, and the amount of ptyalin 
present under the several conditions is indicated by 
such numerical ratios in Table VIII. Reference to this 
table shows that the concentration of the ptyalin in the 
parotid saliva is in all cases (but one) very much in 
excess of that in submaxillary and sublingual glands. 

The total ferment units for each gland are obtained by 
multiplying the rate per minute by the square of the 
length of digested starch. If this be done, it will be found 
that in many cases the deficiency in concentration in 
the submaxillary glands is more than made up for by 
the increased rate of flow, so that it is doubtful whether 
we should continue to regard the parotid gland as the one 
chiefly responsible for the ptyalin content of the saliva. 
The substances are arranged in the order of their 
ptyalin indices (total ferment units from all glands per 
minute), and it will be noted that the order is practically 
the same as that in which they were arranged for the 
inorganic salts. It is observed that acids increase the 
ptyalin index more than ten times that of the " normal 
resting " index. 

It is remarkable that the index for " biscuit saliva " 
* American Journal of Physiology, p. 30. 



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is only increased by 3-6, yet it is for this class of carbo- 
hydrate that the beneficial solvent action of ptyalin is 
most required. Does this not show that the environ- 
mental forces of civilization have not yet produced a 
physiological adaptation to highly artificial or civilized 
articles of diet, as opposed to " natural " foods like 
fruit ? Undoubtedly this is so in a large measure, yet 
not entirely so, for it is seen that the greatest concentra- 
tion of ptyalin from the parotid gland is present in the 
saliva produced by bread and butter excitation ; and 
since the rate per minute is the same for biscuit, bread 
and butter, and alkaline biscuit, there evidently is a 
special stimulus from bread and butter which induces a 
greater secretion of ptyalin. To this extent, then, 
adaptation has occurred, but when the total ferment 
units per minute are compared with those for acid 
biscuit and acid fruits, like apple and orange, it is 
evident how feeble really the adaptation is. 

The mere addition of acid to the biscuit increases the 
ptyalin index eight times. In fact, the ptyalin secretion 
seems to be much more responsive to the stimulus of 
acids than any other constituent of saliva. 

The diminution in the concentration of parotid 
ptyalin from alkaline biscuit is very marked. The 
addition of the soda has reduced it by 47 ; an increase, 
however, in the amount of saliva per c.c. from the 
submaxillary glands makes up for this in the total. 

We cannot but conclude that in this demonstrably 
diminished ptyalin for ordinary starchy foods we have 
one of the potent causes of the present prevalence of 
dental caries. Enormous quantities of carbohydrates 
in such forms are consumed, and, as we shall show, they 
are also the forms which both adhere most to the teeth 
and from which most acid is capable of being formed. 
These are therefore the articles of diet which require the 
greatest solvent action of ptyalin. in order that they 
should be washed away before acid is developed — yet 
they are the ones which receive least. 


Fortunately these experiments also show a way out 
of the difficulty. It is. obviously, to increase the ptyalin 
index by using dilute organic acids incorporated with the 
carbohydrates artificially ; or by the liberal use of acid 
fruits and fresh vegetables, salads, etc.. to raise the 
salivary secretion rate, and also the excitability of the 
salivary glands to weak excitants like bread and biscuit 
(see Table V.). This will have the double effect of 
dissolving the starch and of washing away the resulting 

Regarded from this point of view- — that of cleansing 
the mouth and protecting it from disease — the presence 
of ptyalin in saliva becomes rational and comprehensible. 
It indeed fulfils a function which nothing else could 
possibly do : it renders soluble an insoluble and ad- 
hesive substance like starch, and thus prepares it for 
being naturallv washed away. No substance prepared 
by the wit of man could possibly produce such an effect. 
No dentifrice or mouth-wash can directly remove the 
starch debris in such a manner ; it can only cleanse 
mechanically, and the majority of such artificial 
detergents have, as it has been shown, a depressing effect 
upon the salivary secretion. 

Extirpation of the Salivary Glands. 

The salivary glands have been excised in the dog by 
Fehr.* Minkowski.- and Schafer and Moore. i In all 
cases the animal survived, and the operation produced 
no visible effect, except that in one case it drank more 
water than before. The undigested starch in the faeces 
was not increased in amount, and no sugar appeared in 
the urine. 

Having regard to the fact that pytalin in dog's saliva 

* Archiv fiir Exper. Path. u. Pharmakol, Leipzig, 1S93, 
Bd. xxxi., S. 141. 

* Ibid. 

I Journal of Physiology, Cambridge and London, 1S96, 
vol. xLx.. p. xiii. 


seems at most to be only occasionally present, it seemed 
to the author that this experiment should be repeated in 
an animal which would not drink more water after 
excision of the glands, and in which ptyalin was normally 
present in the saliva. A rabbit was therefore chosen as 
the subject of the experiment. It was found that the 
undigested starch in the faeces was not constant in a 
normal rabbit under ordinary conditions, but varied 
slightly on different days, depending possibly on some 
slight difference in the diet ; but it was also found that 
the undigested starch in the faeces of the rabbits under 
similar conditions varies similarly ; hence, instead of 
comparing the undigested starch in the faeces of one 
rabbit before and after the operation, comparison was 
made with a control rabbit of the same age and weight 
(approximately), and fed on precisely the same food. 

Two white tame rabbits. A and B, were selected, 
their weights being respectively 1119 kilogrammes and 
1 245 kilogrammes. B was anaesthetized with chloro- 
form, and the parotid and submaxillary glands on both 
sides were excised by two curved incisions, about half 
an inch below the inferior margin of the lower jaw (the 
sublingual glands were not removed, since these are 
quite small and very difficult of access in the rabbit 
owing to the narrowness and depth of the lower jaw). 
The wounds were closed and healed aseptically. 

For two days after the operation the interior of the 
mouth (with which the wounds did not communicate) 
was much swollen and inflamed, due. doubtless, to a 
surface infection and to the irritant action of the food, 
since the rabbit's appetite and ability to eat did not 
seem to be at all diminished. This, however, subsided, 
and the rabbit made an uninterrupted recovery- there 
being no difference in any respect between it and the 
control. During the whole time the rabbits were fed 
on as " natural " food as possible — i.e.. grass, clover, 
dandelions, etc. 

Seven weeks after the operation the weights of the 



rabbits were : A = 1/559 kilogrammes, and B = 1-698 
kilogrammes. The faeces of both rabbits were collected 
at intervals, and the undigested starch estimated by the 
following method : 5 grammes of dried and pulverized 
faeces were placed in a flask containing 200 c.c. of 
water and 7 c.c. of hydrochloric acid ; the flask was 
fitted with a condensation tube, and was kept on a sand 
bath at ioo° C. for two days. In this manner any starch 
present became hydrolyzed into glucose. The contents 
of the flask were then cooled, neutralized, and filtered, 
and the filtrate made up to 500 c.c. The glucose present 
in this was then estimated in the usual manner with 
Fehling's solution, the results being expressed in terms 
of starch. 

Four estimations of each were made on each occasion. 
It was found that there was practically no difference 
between the amount of undigested starch present in the 
faeces of A and B. The following were the results of 
three examinations : 

Amount of Glucose 

present in 5 Grammes 

of Faeces. 

I- 3 8 









Mean percentages 
per cent. 

A, 22-403 ; B, 22' 

Expressed as Per- 
centage of Undigested 
Starch in Fasces. 




Difference, 0-07 

It will be observed that on one occasion the per- 
centage of undigested starch in the faeces of B was slightly 
in excess of A, on one occasion A was a trifle in excess 
of B, and on the other occasion both were exactly equal, 
The mean percentages show a difference of 0-07 per cent, 
in favour of B. Having regard, however, to the fact 
that this was not constant, and that the difference is so 
small as to come probably within the range of experi- 


mental error, it may be concluded that the excision of 
the salivary glands did not affect the digestion of starch 
in the alimentary tract. 
. The inference from the results of such experiments 
upon animals is to still further strengthen the conclusion 
that one of the chief functions of ptyalin is to act as a 
protective agent in the mouth, since it has quite a neglig- 
ible value as a digester of starch for absorption in the 

Sulphocyanate of Potassium. 

A considerable divergence of opinion exists as to the 
relationship of a marked amount of potassium sulpho- 
cyanate in the saliva to a relative caries immunity. 

The amount of the salt in human saliva is estimated 
variously as follows : 

o # oooi6 to 0*0084 P er cent. (K salt) — by Oehl.* 
o'oi to 0*014 (Na salt) . . . . ,, Munk.* 

o*oi per cent. . . . . . . ,, Frerichs.f 

o*oo6 „ . . . . . . . . ,, Schmidt and 

0*03 ,, (parotid saliva) . . ,, Mitscherlich.§ 

Ellenberger and Hoffmeister state that it is absent 
from the saliva of the horse, ox, sheep, goat, and pig, 
and that its presence is not constant in the dog. It is 
therefore clear that it is only present in minute quantities 
in man, and that it is absent from many animals who 
are immune to caries. 

Sulphocyanate of potassium is claimed by some in- 
vestigators to exert a continuous disinfectant action 
on mouth organisms, and so lessen the tendency to 

Michel || (of Wurzburg) has tested the saliva of 840 

* Quoted by B. Moore, Schafer's " Textbook of Physiology." 
f Wagner's " Handworterbuch d. Physiologic," iii. 758. 
X Ann. Chem. Pharm., xxix. 156. 

§ Halliburton's " Handbook of Chemical Physiology and 
Pathology," p. 622. 

|| Dental Cosmos, 1909, p. 1278 et seq. 


patients, and finds that the amount of sulphocyanate 
and the incidence of caries are in inverse proportion. 
Low and Beach* examined 300 patients,, and came to a 
similar conclusion. Muntz and Hechtf are of a similar 

Geyger (of Leipzig) recommends the internal ad- 
ministration of the salt in a dose of 0-008 gramme four 
times a day. and claims that thereby the course of 
rapid caries is checked, and the teeth rendered less 
sensitive. In opposition to these views are the investi- 
gations of Florian. Chouppe, Hugenschmidt. Miller, and 
Kirk. These authorities all agree in finding that any 
beneficial action arising from the presence of potassium 
sulphocyanate in the saliva is either entirely absent or 
is only extremely slight. Miller and Kirk are of the 
opinion that the presence of the salt in the saliva 
of persons relatively immune to caries is to be re- 
garded as a coincidence, and not the cause of the 

OppenheimJ found that 0-5 per cent.. 1 per cent., and 
2 per cent, solutions of sulphocyanate had no sterilizing 
effect upon some fermentation bacteria. These solu- 
tions are, obviously, largely in excess of the strength of 
the salt in the saliva. 

In order to test the possible effect of potassium 
sulphocyanate in checking the fermentation of carbo- 
hydrate by mouth organisms, the following test has 
been made : 

Six tubes, each containing 10 c.c. of 2 per cent, 
dextrose (with litmus), were taken, and to five the follow- 
ing amounts of KCXS were added : o-ooi. 0-005. 0-007. 
o-oi, o-i gramme. To the sixth no sulphocyanate was 
added. The tubes were sterilized, and each inoculated 
with 0-2 c.c. of mixed saliva, and then incubated. In 
twenty-four hours all except the o-i gramme tube showed 
an acid reaction (all were faintly alkaline at the start). 

* Dental Cosmos, 1909, p. 1278 et seq. 
f Ibid. % Ibid. 

i ;o 


In forty-eight hours the acid formed was estimated, 
with the following results : . 

Percentage of Sulpho- 
cyanate in each tube. 


Acidity equal to C.C. 
* H 2 S0 4 . 






+ + + 

-r + 

+ + 



Very slight 



At the end of a week the 1 per cent, tube had 
become markedly turbid and acid, and the latter, upon 
estimation, gave a value of 06. Thus it would seem 
clear that sulphocyanate of potassium does exert a 
slight antiseptic action, although it is not sufficient, 
even in a 1 per cent, solution, to act as a disinfectant. 
It does also retard the process of fermentation, and 
lessens the amount of acid production in the strength 
in which it may be found in the saliva — i.e., o-oi per 
cent. — decreasing the acid production in forty-eight hours 
by one-half. Obviously, then, there is a possibility 
that the constant presence of sulphocyanate in the 
saliva may have a beneficial effect, if only it is present 
in sufficient quantity. 

In order to determine whether the concentration of 
sulphocyanate varied with the character of the stimulus 
similarly to other constituents, estimations have been 
made with a similar series of excitants. The percentage 
compositions of the samples of saliva obtained were 
estimated colorimetrically. A series of glass tubes are 
filled with varying percentages of potassium sulpho- 
cyanate from 0-0075 per cent, to 0-03 per cent. One 
tube also is used as a control, containing only distilled 
water. A dilute solution of ferric chloride acidulated 
with hydrochloric acid is added in equal quantities to 


each, the result being varying shades of colour, from 
amber (0-005 P er cent.) to a light port-wine colour (0-03 
per cent.), the control tube having a very light lemon 
colour. These shades are very constant, and are not 
altered by an excess of the ferric chloride. It is ex- 
tremely important to note, however, that a really red 
port-wine colour is not given under 0-04 per cent. 

Ferric chloride solution and hydrochloric acid is then 
added to the saliva to be tested, and after centrifuging, 
in order to clear it, the colour is matched against the 
series of known percentages. In order to eliminate the 
psychic factor, the tubes should be (and were always in 
these estimations) submitted to an independent ob- 
server. The test series of tubes require making up 
afresh each day, since upon standing for some hours 
the colours markedly fade. 

The presence of the sulphocyanate is confirmed by 
the addition of hydrochloric acid causing no change, and 
by the complete discharge of the colour on adding 
mercuric chloride. (The copper sulphate test either 
alone or combined with tincture of guaiacum has not 
been found to be of any value for such small percentages.) 
By the above method differences of 0*002 per cent, can be 
detected without difficulty. 

Bunting* has attempted to show that the ferric chloride test 
as usually performed is practically valueless, for the following 
reasons : 

1 . That the colour reaction obtained with ferric chloride is 
much more reliable in an ether solution of sulphocyanate than 
a water solution, so much so that an ether solution of dried 
saliva should always be made. 

2. That other substances besides sulphocyanate may be 
present in the saliva which give a similar red reaction with 
ferric chloride. 

I am not prepared to accept Dr. Bunting's theories. 

1 . Is the ethereal solution more reliable than the watery 
solution of potassium sulphocyanate ? The following simple 
tests give the answer in the negative : 

(a) Equal parts of sulphocyanate are dissolved in equal 
amounts of ether and water in separate tubes, the same amount 

* Dental Cosmos, December, 1910. 


of ferric chloride solution is added to each, and a red colour of 
equal intensity develops in both. 

(b) A water solution of sulphocyanate is made, an equal 
quantity of ether is added, and the whole well shaken. Ferric 
chloride is added, and only the lower or water solution takes a 
red colour — i.e., the ether had abstracted hardly any sulpho- 

(c) An ether solution of sulphocyanate is made, an equal 
quantity of water added, and the mixture well shaken. Ferric 
chloride is added, and the lower half (the water) is a deep claret 
red, whilst the upper (the ether) is only a light magenta — i.e., the 
water has abstracted nearly all the sulphocyanate from the 

(d) Similar results exactly are obtained if the ferric chloride 
be added before shaking the mixture, and the colour can be 
seen gradually passing from the ether to the water. 

2. Is the possible presence in the saliva of other substances 
which give the ferric chloride test a serious source of error ? 
Xo, and for the following reasons : 

The substance mentioned by Dr. Bunting is aceto-acetic acid. 
This acid is formed in the body in the course of diabetes only, 
and when it is present it is usually regarded as of very grave 
significance, and it is hardly likely that anyone would obtain 
the saliva of such a person for analysis without being aware of 
the general condition. Moreover, if it is present, the simple 
procedure of heating the saliva decomposes it and renders it 
negative to the ferric chloride test. 

Aceto-acetic acid is, too, very soluble in ether, and this 
lessens the value of the ether test. 

Other substances which give the ferric chloride test are the 
metabolized products of salicylic acid, carbolic acid, antipyrin, 
and thallin, and it is at present quite an assumption that these 
products are secreted by the salivary glands. Moreover, if it 
should be found that they are so secreted, it is a very simple 
thing to ascertain from the patient whether any such drugs are 
being taken. 

Table IX. gives the sulphocyanate estimations 
obtained by the usual series of stimulations, the saliva 
from all the glands being collected in one receptacle. 

It is clear that the concentration of sulphocyanate is 
very little affected by the nature of the substance being 
eaten, the percentage composition being remarkably 
uniform with the exception of orange, which causes a 
rise of 0-0025 P er cent. In this respect the sulpho- 
cyanate differs from the other constituents of saliva. 
Owing, however, to the increased or decreased amount 



of saliva per minute, the total amount of sulphocyanate 
in the mouth per minute varies greatly. Here also 
acids give the greatest amount, bitters and sweets the 
next greatest, whilst alkalies cause a diminution. 

We have shown previously that sulphocyanate has 
an inhibitory effect upon lactic acid fermentation ; if, 


Potassium Sulphocyanate. 



Total Amount 

of Sulpho- 

Amount of 


Substance masticated. 



per Minute : 

in Mixed 







Biscuit (normal) 




+ Na 2 C0 3 2 per cent. 




+ quinine 




+ saccharine o-o 1 per 



7 -40 


+ acid potassium tar- 

trate 0-5 per cent. 










I i-oo 


therefore, it is wished to increase this effect, and not to 
diminish it, it is obvious that acids should be used and 
alkalies withheld. 

Effect of Internal Administration. 

1. In Animals. — {a) A dog, weight 25 kilos, was given 
6 milligrammes of pilocarpine by hypodermic injection. 
Ten minutes after the saliva was collected by aspiration 
from the mouth, and tests for sulphocyanate were entirely 
negative. 2-5 c.c. of 1 per cent, sulphocyanate were 
then given per os (this being three times the dose 
advocated by Greyger for children). Specimens of 
saliva were collected five, ten, forty-five, and seventy 


minutes afterwards, and in no case could even a trace 
of sulphocyanate be observed. 

(b) A similar experiment was performed on a smaller 
dog, with corresponding doses. The results were 
exactly the same. 

(c) A rabbit was given i milligramme per kilo body- 
weight of pilocarpine hypodermically, and five minutes 
afterwards the saliva, upon being tested, gave a nega- 
tive result for sulphocyanate; 0-2 gramme potassium 
sulphocyanate was then given, the rabbit was allowed 
to eat grass for ten minutes, and the mouth was 
swabbed out with distilled water. The saliva was then 
collected by aspiration, and showed sulphocyanate to 
be present to the extent of 0-035 P er cent. Half an 
hour afterwards the percentage was the same, and in 
one and a half hours it was still 0-03 per cent. 

2. In Man. — The following experiment illustrates the 
effect of the internal administration of potassium sul- 
phocyanate in man : 


Resting saliva contained (three estimations 

on three days) . . . . . . . . . . coioo 

o-i gramme KCNS taken in water, and the 
mouth well rinsed out — 

5 minutes aiterwards the saliva contained 0*0150 

15 ,, ,, ,, ,, 0*0150 

20 ,, ,, ,, ,, 0*0150 

60 ,, ,, „ ,, 0-0175 

3 hours ,, ,, ,, 0*0200 

The percentage in resting saliva remained at 0*02 per 
cent, for seven days afterwards. It would not be 
correct, however, to say that this was due to the reten- 
tion of sulphocyanate in the system ; it may have 
been, or it may have been due to other unascertained 

It is therefore concluded that in man and some 
animals, but not in others, the amount of sulphocyanate 
in the saliva may be rapidly increased by internal 
administration ; and that advantage of this may be 


taken in cases where a continuous antiseptic action is 
desirable, such as in the rapid and acute caries of 

The drug is not an active poison,* and may be given 
advantageously in repeated doses of J- to 1 grain. 

Origin of Potassium Sulphocyanate. 

Undoubtedly the sulphocyanate in the saliva is a 
product of protein metabolism ; but whether it is, as 
Fenwick f has suggested, to be regarded as a measure of 
the protein metabolism of the body seems not to be 
proved. An appreciable amount of protein in the form 
of mucin, epithelium, leucocytes, etc., is split up in the 
mouth into simpler compounds by the action of bacteria, 
and the question arises, Is sulphocyanate of potassium 
one of the compounds formed ? 

The following observations tend to show that this is 
the case : 

(a) The percentage of sulphocyanate in mixed saliva 
from the mouth is always higher in the morning, before 
the teeth are cleaned, than it is shortly after cleaning 
and rinsing the mouth, the excess in the case of the 
author varying from 0*005 to 0-02 per cent., and in 
the case of another individual there was a differ- 
ance of 0*0125 P er cent. 

(b) Mixed saliva collected from the glands direct 

* Ninety grains have killed a rabbit in four hours. There 
were convulsions in the case of a rabbit which died from 
i£ drachms of a strong solution after ninety seconds. In other 
cases rabbits took 3 drachms without any injurious effects 
(Mayer-Tidy). The appearances after death were similar to 
those produced by the action of an irritant poison. 

Westrumb (Tidy) found that 40 grains killed a dog in seven 
minutes, and another in two hours, convulsions being the promi- 
nent symptom, and the poison was found in the blood, lungs, 
liver, spleen, and kidneys. 

Soemering found that 30 grains killed a dog in one minute. 

f " The Saliva as a Test for Functional Disorders of the 
Liver," i88q. 


contains a lower percentage of sulphocyanate than does 
the saliva from the mouth before or afterwards. 
As instance the following series of estimations : 

Per Cent. 
Teeth uncleaned for twenty-four hours .. KCNS =0-0150 

Saliva from glands direct (orange) . . . . ,, = o-oioo 

(apple) .. .. ,, =0-0075 

Saliva from mouth immediately afterwards ,, = o-oioo 

Teeth cleaned and mouth rinsed . . '. . ,, = 0-0075 

(c) The amount of sulphocyanate in saliva increases 
upon incubation. 

Per Cent. 
Saliva collected after cleaning the teeth and) T, n ^ c 

rinsing the mouth J K( - Nb = 0-0075 

Divided into two equal portions and incu- 
bated — 

In 24 hours .. .. .. .. KCXS = 0-0150 

In 48 . . . . . . . . = 0-0175 

(d) More sulphocyanate may be obtained from the 
precipitate of centrifuged saliva than from the clarified 
portion. (This,, however, does not seem to be con- 

(e) Traces of sulphocyanate may be developed in 
broth infected with mouth organisms. 

It therefore would appear that in the bacterial metab- 
olism of the precipitated organic constituents of saliva 
we have another active protective agency, and one 
which appears to be specially adapted to afford pro- 
tection during the night, when oral circulation is reduced 
to a minimum. I have noticed, too. on several oc- 
casions, that the organic constituents in saliva from 
immunes separate out much more quickly than they do 
in saliva from susceptibles. 

Reference has been made to the associations between 
percentage of sulphocyanate and immunity to caries 
(see p. 169). I have not made many observations in 
this direction ; but such as they are they do not entirely 
accord with the findings of Michel, Low, and Beach ; but 


the numbers are too small to make any definite deduc- 
tions. For instance — 

Per Cent. 

Immune No. 1 . . . . KCNS = 0*0300 

Xo. 2 . . ,, = 0-0250 

No. 3 . . . . ,, = 0*0125 

Susceptible No. i, j 

until recently quite - .. ,, =0*0075 

immune J 

o ,-u xt ~_~.«-fAll carious 

Susceptible No. 2 .. „ = 0*0125 | cayities had 

x°' 3 •' " = °'°T 1 been filled in 

^°-4 •• - = ' 0100 I these mouths. 

Waugh* has recently claimed that sulphocyanate has 
the property of preventing organisms from forming 
adhesive plaques. His experiments are. however, 
somewhat inconclusive, since ten tubes of broth to 
which sulphocyanate had been added, infected with 
mouth organisms, showed no plaque formation, but of 
ten control tubes only one showed plaque formation. 
The addition of carbolic and cassia to the broth caused 
an increase in plaque formation, but when sulphocyanate 
was also added this was slightly decreased. 

Conclusion. — On the whole, we may conclude that 
whilst undoubtedly sulphocyanate of potassium is a 
beneficial element in saliva, and one making for free- 
dom from disease, yet it cannot be regarded as the most 
important or only factor in producing a natural immunity 
to dental caries or oral sepsis. 


There can be no doubt but that the phosphates of the 
saliva have a protective action upon the teeth. Lactic 
acid readily combines with phosphates to form harmless 
lactates, and the lactic acid will be more readily and 
rapidly " satisfied " if the phosphates be in solution 
than if they are in a solid and extremely hard mass, like 

* Dental Cosmos, February, 1910, p. 173. 

1 7 8 


Reference has also been made to another probable 
protective function of phosphates in penetrating and 
hardening the outer strata of enamel after eruption. 
Therefore the phosphate content of saliva must be of 
importance in considering the matter of immunity to 
caries. The question then arises. Are the phosphates 
subject to the same variations as the alkaline salts, and 
can they be increased or decreased at will ? In order 



Total Amount 


Amount of 

of Phosphates 

Substances used as Stimulant. 

as P 2 5 


per Minute: 

per C.C. 











+ Sodium carbonate 

2 per cent. 




,, + Sodium chloride 2 

per cent. 




+ quin. sulph. 1 in 800 




+ acid potassium tar- 

trate o"5 per cent. 

and saccharine 

0*01 per cent. . . 








Biscuit, + tartaric acid 1 per 













to determine this point, the phosphates present in the 
saliva obtained by various stimulants were estimated. 
(The method adopted was that of titration with § 
uranium nitrate. The saliva was diluted, and there was 
added a small quantity of sodium acetate acidified with 
acetic acid. The indicator used was potassium ferro- 

Table X. gives the results of such estimations. The 


saliva was collected from the glands direct during masti- 
cation, and both tubes were run into one receptacle. 

It will be observed that both the amount per c.c. and 
the amount per minute vary considerably according to 
the substance being eaten. Again, the addition of an 
alkali causes a diminution ; sodium chloride slightly 
increases the amount, and so does a bitter flavour, but 
not to the extent that an acid-sweet taste does ; and a 
pure acid flavour, like tartaric acid, is more efficacious 
still. " Natural " excitants, however, like apple and 
orange, here also produce the greatest amount of the 
salts per c.c. ; and since these also produce a great 
increase in the total amount of saliva, the increase in 
the total phosphates per minute is still more marked. 
It is seen that the addition of sodium chloride increases 
the total phosphates per minute more than double ; that 
apple and orange treble and quadruple the amount 


The function of sodium and potassium chlorides in 
saliva is probably largely protective to the mucous 
membrane of the mouth, and also they undoubtedly 
increase the sapidity of ordinary articles of diet, and 
thus induce a further reflex flow of saliva. 

It is well known, for instance, that washing the mouth 
out with a weak solution of common salt increases the 
perception of other substances — such as sweets. Estima- 
tions of the amount of chlorides present — as sodium 
chloride — in the saliva under various conditions have been 
made, and the results tabulated in Table XI. 

The method used was as follows : 

About 10 c.c. of mixed saliva were collected with the 
segregator and cannula, the mucin removed by precipita- 
tion with acetic acid. One c.c. of nitric acid and a 
known volume of standard silver nitrate were then added ; 
the silver chloride was removed by filtration, and the 
amount of free silver nitrate remaining in the filtrate 



was estimated by titration with a standard solution of 
ammonium sulphocyanide. By deducting this from 
the amount of silver nitrate originally used, the amount 
used in combining with the chlorides is obtained, and 
from this the weight of the chlorides, as sodium 
chloride, is readily calculated. It is seen upon refer- 
ence to the table that the amount of chlorides present 


Chlorides. (Estimated as Sodium Chloride.) 

Total Saliva during Stimulation. 

Substance Masticated or 

used as Stimulant. 

C.C. per 

Grammes NaCl 

Grammes NaCl 


per C.C. 

per Minute. 

Normal saliva (resting) 




Biscuit (normal) 




,, + Sodium carbon- 

ate 2 percent. 




,, +Quinine sul- 

~ phate i in 800 




,, +NaCl 2 per cent. 




„ + Acid tartrate of 

potassium 05 

per cent, and 


001 per cent. 




,, -f Tartaric acid 1 

per cent. 












under active stimulation conditions is in excess of 
what has been found for other salts — both in amounts 
per c.c. and per minute ; for various stimulations it 
follows closely the order obtained for other constituents. 
The acid-flavoured biscuit and acid fruits give the highest 
amounts per c.c. and per minute ; whilst again the 
alkaline biscuit gave a subnormal amount both per c.c. 
and per minute. The sodium chloride biscuit increased 


the amount per minute by seven times. It was thought 
that possibly to this form of stimulus the chloride 
content might not have been raised, but that evidently 
is not so ; in fact, a greater response is obtained than is 
the case for either alkaline salts or phosphates. 

In addition to the sedative and protective effect of 
the chlorides upon the mucous membrane of the mouth, 
doubtless the marked increase and excess of chlorides 
over other salts, and especially over the alkaline salts, 
serves the very necessary purpose of counteracting the 
depressant effect which an increase of the latter by 
themselves would be bound to bring about on the 
gustatory nerves. 

For instance, the alkaline salts for biscuit and orange 
stimulations are as i : 5-5 (cf. Tables I. and II.) ; but the 
chlorides for the same stimulations are as 1 : 7*9. Thus 
the effect of an increased stimulus tends not to be auto- 
matically cut off when the excitant is removed, but 
rather to be perpetuated. 


The amount of mucin present in saliva is not of so 
much importance as the condition in which it is present. 

In the ordinary viscous condition in which it is present, 
it is undoubtedly to be regarded as being favourable to 
the development of dental caries and oral sepsis, in so 
far as it forms a sticky mixture with carbohydrates, 
binds them to the teeth and tissues, and thus facilitates 
the prolonged action of the incorporated organisms. 
It has been suggested that mucin is a source of mucic 
acid, which may attack the enamel. Cook.* however, 
has shown that this conversion into mucic acid can 
only occur under aseptic conditions, which certainly 
cannot obtain in the mouth. Mucin by itself in the 
presence of mouth organisms undergoes an alkaline 
decomposition, and is therefore to be regarded as a 
* Johnson, " Operative Dentistry," p. 477. 


protective agent. This I have repeatedly observed, 
and it may be demonstrated in the following manner : 
Saliva is collected, and the mucin precipitated with 
dilute acetic acid and filtered. The precipitate is 
dissolved with warm sodium hydrate, litmus is added, 
and the solution just brought to the neutral point by the 
addition of acid. The solution is now infected with 
mouth organisms and incubated, an alkaline reaction 
rapidly develops, and in two days may be equal to as 
much as 27 units (f$ H 2 S0 4 ) per c.c. This is much more 
likely to take place in the mouth, and the resulting 
alkalinity to be greater and more efficacious, in the case 
of mucin precipitated in a solid state on or around the 
teeth. Such precipitation is produced by all weak acids 
and by acid salts, notably by acid potassium tartrate,* 
and flakes of solid mucin rapidly separate out and cling 
to any solid substance. This undoubtedly is, I think. 
the source of some of the " plaques " found upon teeth. 
Such plaques would, of course, be subsequently dis- 
solved by the increased flow of highly alkaline saliva. 

Mucin is also precipitated from stagnant saliva to a 
lesser extent, and in a less solid form, upon the escape of 
carbon dioxide and the consequent precipitation of 
some of the alkaline salts ; and where the salivary secre- 
tion is deficient the viscous mucin clinging to the teeth 
does not tend to be redissolved on account of the 
decreased alkalinity of the saliva. This, I think, prob- 
ably explains the difference between the different kinds 
of " plaques " observed. The ones which are " actively " 
precipitated by acids are firmer and more compact ; 
those " passively " precipitated by stagnation are softer 
and more viscous, or " gelatinous." 

When the mucin is precipitated by acids or acid salts, 
alkaline salts are also carried down, incorporated with it. 
and it is almost impossible to render the flakes of mucin 
acid even by the addition of large amounts of acid. The 

* Kirk has also since noted that mucin may be precipitated 
by acid sodium phosphate. 


teeth in this way become coated with an organic alkaline 
film, which acids have the greatest difficulty in pene- 

On the other hand, if fermentable carbohydrates are 
incorporated in the mucin, the organisms attack these in 
preference to the mucin, and thus an acid reaction 
develops until all the carbohydrate is used up. Another 
advantage derived from the active precipitation of 
mucin is the elimination of a strong, non-electrolyte 
from the saliva, thus facilitating dialysis of its inorganic 
salts. There is manifested also another beneficial action 
of mucin when acid substances are being masticated. 
All the particles seem to be more closely bound together 
■ — united to the central lobes- — so that when the latter 
are swallowed practically all the particles follow, and do 
not remain isolated and adherent to the teeth, as happens 
with such articles as bread, biscuits, or " sweets." 

The association observed clinically between ropy 
saliva and acute caries in children may be due to one 
or a combination of all of three causes : (1) It may be a 
special characteristic of chronic pain associated with a 
" nervous " or mental effect ; (2) it may be due to the 
original cause of the caries — i.e., a too liberal consump- 
tion of " free " sugar ; (3) it may result from a deficient 
alkalinity of the saliva. It may possibly be regarded 
as an effort by Nature to provide a material which, if 
precipitated, would undoubtedly protect painful sur- 
faces against acid stimuli. 

A few estimations of the amount of mucin present 
under various conditions have been made, but the 
technical difficulties are considerable, and a satisfactory 
method for all substances has not yet been found. 

The difficulties arise from the fact that about 80 per 
cent, of the mucin in mixed saliva comes from the buccal 
mucosa, and hence is very difficult to collect. This has 
been attempted by masticating substances, expectorating 
the bolus, and filtering through muslin. Ten c.c. of 
the filtrate were then taken, mixed with a large excess 


of 0-5 per cent, sodium hydrate solution, allowed to 
stand for some time in order to dissolve the mucin, again 
filtered ( through paper filters) ; acetic acid was added to 
precipitate the mucin, and the latter collected on a dried 
and weighed filter-paper. The precipitate was then 
washed with 2 per cent, acetic acid, alcohol, and ether, 
and the filter-paper again dried and weighed. The 
mucin from saliva collected by expectoration immedi- 
ately after mastication has also been similarly esti- 
mated, and the results in the two cases were so close 
that the average of the two is given in Table XII. 

In the case of apple, orange, biscuit, and sugar (cane). 



Substance used as Stimulant. 

From Glands 

Grammes .. 

From whole 

Grammes \. 

Difference = 

from Buccal 


Normal saliva resting 









0-2 5 



0-2 4 I 





it is seen that the amount of mucin from the whole 
mouth is greatly in excess of what is obtained from the 
salivary glands direct ; the difference between these two 
gives the amount derived from the buccal mucosa. 
There is not a great deal of difference between the several 
amounts for biscuit, apple, and orange, but sugar 
evidentlv is a much more powerful excitant of the 
mucous glands than weak acid substances ; roughly, 
three times the amount being secreted. Sugar and 
biscuit, of course, do not precipitate the mucin at all, 
but. on the contrarw form with it an exceedingly stickv 
and viscous mass. This will be referred to again later, 
but is strikinglv exemplified when attempting to filter 




masticated mixtures of biscuit and saliva, and apple 
and saliva, for instance. The saliva from the apple 
mixture passes through the filter readily, but from 
the biscuit or sugar mixture filtration is either exceed- 
ingly slow or does not occur 
at all. Similar conditions, of 
course, obtain in the mouth, 
where the crevices between 
the teeth may be regarded as 
the filter. 

The constant consumption 
of "sugar" must therefore, by 
continual stimulation, cause a 
hypertrophy of the mucous 
glands, and give rise to a 
higher mucinous secretion in 
the mouth, and doubtless ac- 
counts to some extent for the 
hypersemic and swollen con- 
dition of the mucous mem- 
brane so frequently seen in 
people who consume much 
"sugar" in its artificial forms. 

For the estimation of mucin 
for clinical purposes I use a 
long glass tube, graduated at 
the upper end, and with a 
cork in the lower end (see 
Fig- 53) • The saliva is poured 
in, and 20 per cent, acetic acid 
is added until the level of the 
graduations is reached. The 
mucin is rapidly precipitated 
and rises to the top ; on stand- 
ing, the precipitate condenses, and the amount may be 
read off in one hour. Each division on the tube equals 
approximately 0-002 gramme of mucin. This is not 
absolutely exact, however, since a small but variable 


Fig. 53. — Mucinometer 
(for Approximate Esti- 
mations only). 


amount of epithelial debris and carbon dioxide gas are 
usually included amongst the precipitated flakes of 

Salivary Stimulants not Previously Considered. 

Effect of Pyrethrum. — It is well recognized that pyre- 
thrum has a stimulating effect upon the salivary glands, 
and this investigation would not be complete without 
a reference to its action. 

Its effect on the secretion of saliva has been tested in 
a similar manner to other substances, but. as will be 
readily seen from the figures, its power as a salivary 
stimulant cannot compare with that of acids. 

A biscuit was treated with a 2 per cent, mixture of 
tincture of pyrethrum and water, and the saliva col- 
lected during mastication, with the following results as 
regards amount and alkalinity : 

P*rn,iH Subma f lar >" Total from 
.Parotid. and ,, ~, , 

Sublingual. a11 Glands - 

Amount per minute 
Alkalinity per c.c. 
Alkalinity per minute 

0-15 3-30 6-90 

r6o o-68 0'72 


Comparing this with similar stimulations given in 
Table II.. it is seen that pyrethrum used in this manner 
ranks very little higher than oil of cloves, and is not so 
efficacious as sodium chloride. The low alkalinity of 
the submaxillary saliva is particularly noticeable. 

The solution of pyrethrum used was much stronger 
than could be used with comfort by itself, but combined 
with the biscuit its effect was less marked. The mouth 
was washed out for one minute with 10 c.c. of a 1 per cent, 
mixture of tincture of pyrethrum and water, this being 
the maximum strength which can be used without dis- 
agreeable effects. Five minutes afterwards the saliva 


was collected by expectoration, and showed a total 
secretion of 2*2 ex. per minute, and an alkalinity index 
of 2-28 — a definite increase over the " normal resting," 
but not a very marked one, and not so great as that 
produced by acid mouth-washes, as will be shown 
subsequently (see p. 230). 

Pyrethrum also produces a greater secretion of mucin, 
probably by its obvious stimulating effect upon the 
buccal mucous membrane ; and since this mucin is not 
precipitated, it must be regarded with disfavour. After 
washing the mouth out with the 1 per cent, mixture of 
tincture of pyrethrum and water, the saliva contained 
0*29 per cent, of mucin. 

Pyrethrum in strong solutions is certainly a powerful 
salivary stimulant, but it is then without the range of 
practicability, since certainly no one could be persuaded 
to use it, owing to its prolonged and extremely disagree- 
able effect on the tongue and oral mucous membrane. 

As a therapeutic agent in special cases it may be 
useful, but it cannot be recommended either as a 
flavouring agent for food or as a routine prophylactic. 

The Stimulus of Pain.- — The effect upon the salivary 
glands of painful sensations within the mouth is 
know r n to be stimulating. The question has not been 
properly investigated, but probably both the situation 
and the character of the pain have definite effects upon 
the amount and composition of the resulting secretion. 
The following is an analysis of mixed saliva obtained by 
aspiration during the operative treatment of a lower 
premolar : 




Potassium sulphocyanate 




Per Minute. 
2'2 C C C 

171 -(c.c.^NaOH). 

23*04 units. 

o'ooi6 gramme. 




It is therefore chiefly a watery saliva, both organic and 
inorganic constituents being markedly low. 


The Effect of Alkalies and Acids on the Dialysis of Saliva. 

We have before alluded to the probable function of 
Xasmyth's membrane and its action as a dialyzing 
membrane, and therefore the important role it plays in 
the hardening of the superficial layers of enamel after 
eruption. We have also shown how various substances 
promote a flow of saliva of varying character, and have 
noted the effects of various chemical substances upon 
the constituents of saliva, amongst the most important 
being the fact that alkalies added to saliva cause a pre- 
cipitation of the phosphates and a retention of the mucin 
in solution, whilst acids have an exactly reverse effect. 
If this be so. the addition of an alkali to saliva should 
materially reduce the amount of phosphates, which 
would dialyze through Xasmyth's membrane, but the 
addition of acids would increase the amount. 

The following is experimental evidence that such 
action is possible and extremely probable : 

Thirty c.c. of mixed saliva were taken and divided 
into three parts — A. B. and C. To A nothing was added, 
and it acted as a control ; to B was added 0-04 gramme 
of sodium carbonate, and to C a similar amount of acid 
potassium tartrate. Dialyzers (the membrane being of 
sheep's intestine) were then placed in each, and filtration 
avoided by means of 0-45 per cent, sodium chloride inside 
the dialyzers. Dialysis was allowed to proceed for five 
days, and the amount of phosphates which had passed 
through the membrane in each case estimated. The 
following table expresses the result : 

Amount of Phosphates as P2O.5 
dialyzed in Five Days. 

A, Control . . . . . . . . 0-00080 gramme. 

B, Saliva+ sodium carbonate .. 0*00025 

C, Saliva+ acid potassium tartrate 0.00130 
Each 10 c.c. of saliva originally 

contained .. .. .. .. 0*00530 

It is observed from this that the addition of the 
alkali has diminished the normal amount of phosphate 


which should dialyze by more than two-thirds, and that 
the addition of the acid salt has increased it by more 
than one and a half times ; also that, approximately, in 
the control one-seventh of the total phosphates have 
dialvzed. in the alkali saliva only one-twentieth, but in 
the tartrate saliva one-fourth of the whole have passed 
across. The latter result is due, of course, to the 
phosphates being held in solution instead of being more 
or less precipitated, as in A and B, and also to the 
elimination of the non-electrolyte mucin by its pre- 

Although membranes differ in their dialyzing powers 
— and Nasmyth's membrane may differ in this respect 
from sheep's intestine — there is no reason to doubt that 
the relative proportions for the same salts would be the 
same in each. 

The Possible Presence of Immune Bodies. 

This subject was investigated by Miller,* who came 
to the conclusion that the protective bodies of the normal 
blood-serum do not under normal conditions pass into 
the saliva in sufficient quantity to be detected by 
ordinary means. Yet there is some evidence that 
immune bodies do pass into the saliva. For instance, 
it is known that snake-charmers, by allowing themselves 
to be bitten by snakes of increasing size, acquire a high 
degree of immunity to the snake poison ; and, further, 
that the saliva of such persons applied to the bite of a 
snake in another person has a beneficial action. 

Secondly, it is known that in acute diseases, like diph- 
theria, cholera, and pneumonia, the saliva exerts a 
deleterious effect upon the particular organisms con- 
cerned. Therefore it would seem to be proved that it 
is possible for immune bodies, or antibodies, to be 
present in the saliva. 

The question then arises as to whether there are any 
* Dental Cosmos, 1903, p. 1. 


such bodies present in the saliva of persons immune to 
dental caries, and whether they are present in sufficient 
quantity to account for the immunity. The importance 
of " opsonins " in the blood as a factor in immunity has 
of recent years been widely recognized, and there seems 
no reason why opsonins should not pass to some extent 
into the saliva, where they might exert a deterrent 
effect upon the development of the mouth organisms. 

Estimations of such action in the saliva have been 
commenced, working along the ordinary opsonic index 
methods. Leucocytes are obtained by centrifuging 
blood, and washed in the usual manner. About 2 c.c. 
of the saliva to be examined are then taken and centri- 
fuged for three or four minutes ; the epithelial debris 
and some of the mucin will be deposited, leaving an 
opalescent upper portion, which still contains a large 
number and variety of organisms. This cleared saliva 
is taken as representing both the bacterial emulsion and 
the fluid (serum) containing the opsonin. Equal 
volumes are then obtained • of cleared saliva and 
washed leucocytes, and after being well mixed the 
whole is incubated for fifteen minutes. Smears are 
then made in the usual manner, stained with Wright's 
stain, and the number of organisms taken up by the 
leucocytes counted. 

The method has very obvious imperfections and 
difficulties, not the least of which is the fact that saliva 
is not isotonic with blood-serum, and hence the cor- 
puscles are distorted, and sometimes broken up. 
Attempts to make the saliva isotonic by the addition 
of solution of sodium chloride have not been very 
successful, since, as has already been shown, the 
saliva varies so much in composition. The mucin, too, 
in the saliva, there is reason to believe, interferes with 
the phagocytic action of the leucocytes. 

A fair number of " counts " have been made, chiefly 
with the saliva of three individuals, one of whom (A) is 
nearly immune to caries (i.e., aged twenty-five, and 


having only one or two small carious cavities previously 
filled) ; one (B) is susceptible to a slight degree, and the 
other (C) is susceptible to about the average degree. 
In all of these phagocytosis on every occasion was 
extremely feeble, although there were always plenty 
of organisms present. 

Organisms and leucocytes are frequently seen in close 
pioximity, yet not one organism may be absorbed by 
the leucocytes. Again, when phagocytosis does occur, 
it does so very irregularly. 

The results of these estimations are as follow : 

A's phagocytic index = 0*56 ) — ,. . , 

-g, r ° J _ Q .^g I^To the mixed organisms 

C's " ,',' =o-i6j of the mouth. 

One could not from these calculate an " opsonic index " 
for the various salivas. It does not even prove, although 
it suggests, that the increased phagocytosis of A was due 
to the presence of opsonins in the saliva ; the increase 
might have been due to a difference in the chemical or 
physical nature of the saliva. It does indicate, however, 
that there is either the presence or absence of some 
substance in the saliva of a relatively immune individual 
which facilitates phagocytosis. 

Phagocytosis, however, does not occur normally in the 
saliva to any appreciable extent. It is well known that 
" altered " leucocytes are normally found in saliva, and 
the fact of their being altered is due, most probably, to 
the saliva being hypotonic to blood-serum. An examina- 
tion of the deposit in centrifuged saliva stained with 
Wright's stain reveals many such leucocytes, but I have 
not been able to satisfy myself of any evidence of active 
phagocytosis (in mouths free from suppuration). 

Epithelial Debris. 

Mixed saliva from the mouth always contains large 
numbers of squamous epithelial cells, and, in marked 
contrast to the leucocytes, these are always loaded 


with organisms. Fig. 54 shows such a cell crowded 
with organisms, and two leucocytes also (slightly 
out of focus) which contained no organisms. The 
organisms are, of course, merely lying on the epithe- 
lial cells ; but whether the saliva be centrifuged or not, 
by far the greater number of organisms present in any 
film are always attached to an epithelial cell. It does 
not seem at all likely that these are only the organisms 


.. .. 

Fig. 54. — Epithelial Cell from the Saliva loaded with 

which grew against that particular cell before it des- 
quamated ; it would seem to be far more probable that 
there is some attraction, simply physical, or maybe 
" vital,' ' by which the organisms are collected on the 
cell. At any rate, there can be no doubt that these cells 
act as carriers of organisms, and that as a rule they carry 
them to destruction in the hydrochloric acid of the 
stomach. In this manner they must rank as one of the 
chief factors in keeping down the number of organisms 


in the mouth. Therefore articles of diet which are 
" demulcent " in character tend to prevent the exercise 
of this function, as also do other articles, such as pure 
cane-sugar, which excite a strong secretion from the 
mucous glands, and so by preventing friction lessen 

If the epithelial cells are not swallowed, they are 
digested by the organisms upon them, and thereby 
alkaline decomposition products are formed. 

Abnormal Constituents. 

Urea, ammonia, lactic acid, leucine, traces of bile acids, 
bile pigments, glucose, and glycogen have all been de- 
scribed as present occasionally in the saliva.* These, 
when present, have only been found in minute quantities, 
and most of them from the present point of view are 

The two carbohydrates, however, might be of extreme 
importance. The presence of glycogen has been con- 
firmed by Michaels f in some individuals in considerable 

I have no evidence to disprove this statement, but, 
bearing in mind the fact that glycogen is rapidly con- 
verted into maltose and isomaltose by ptyalin, it is 
a little difficult to conceive how the two could be present 
together, secreted by the same glands. They are 
physiologically incompatible. There are two possible 
explanations : (1) That ptyalin is absent entirely from 
the saliva of those persons in whom glycogen is said to 
be present. (2) That the glycogen is present by con- 
tamination with the mouth, since it is found in pus, 
in pathological growths, and in fungi. J In order to 
be absolutely sure of its presence in the saliva, the 

* Gamgee, " Physiological Chemistry " ; Schafer, " Textbook 
of Physiology." 

f " Sialo-Semeiology," Paris, 1900. 

I Various authors quoted by Halliburton in Schafer's " Text- 
book of Physiology," p. 15. 



latter would need to be collected from the glands 

As regards glucose, some observers state that this is 

- -:;t in the saliva in cases of diabetes.* whilst others 
deny this.- Carlson and Ryani have shown that traces 
of glucose are normally present in the saliva of the cat. 
but failed to demonstrate its presence in man in a case 

: ;::.. r::~ 
I have examined the saliva for glucose in a number 
of healthy and sick persons, but on no occasion has 
even a sign of it been present. The diseases from 
which the patients were suffering were : diabetes, 
pronounced and mild : nephritis, acute and chronic ; 
Graves' disease : typhoid fever phthisis : gastro- 
enteritis : anaemia : oral sepsis gastritis and fleeting 
joint pains) ; neurasthenia : cystitis : aneurysm ; loco- 
motor ataxy, and syphilis. There was. of course, no 

- n to suppose, except in the diabetes cases, that the 
saliva would contain glucose ; but in view of the fact 
that these patients all exhibited more or less oral 
sepsis, it is important to be able to show that the 
primary source of the lactic acid was not in the saliva 
itself — as. indeed, has been suggested. 


i. It is evident that the saliva is a fluid extremely 
variable in its composition and amount, but that these 
variations do not occur without reason, but rather in 
obedience to fixed and definite laws and in respon- 
certain ascertainable stimuli. 

2. The mechanism controlling salivary secretion is ex- 
tremely sensitive and complex, since different " flavours " 
of little intensity are capable of being " selected." and 

* Fleckseder, Cent ralblatt fur innere Medici n, 1905, vol. x.\ -. : 
p. 41. 

A Mosler. Archiv tur Heilkunder. 

A .erican Journal of Physiology , April I, 1908. 


give rise to secretions of saliva differing widely in 
character and amount. 

3. That practically all the normal constituents of 
saliva are. if present in sufficient amount, of value and 
importance in protecting the teeth against the occurrence 
of dental caries, and in maintaining the health of the 
oral mucous membrane. 

4. That acids, and particularly the " natural " 
organic acids, are the stimulants which excite the 
greatest amount of these protective substances per 
minute, and. moreover, give rise immediately, and for a 
considerable time afterwards, to an increased alkalinity 
of the mouth. That, conversely, substances of little or 
no distinctive " flavour." and also alkalies, produce a 
diminution in the amount of protective substances per 
minute, and reduce the alkalinity of the mouth both at 
once and for some time afterwards. 

5. That in the saliva is provided a natural and 
potentially perfect mouth-wash acting continuously day 
and night (not merely for a few minutes a day). That 
it is. moreover, completely under control ; that it may be 
altered or varied in amount or composition ; that its 
beneficial effects may be increased or decreased absolutely 
at will. 



dioxide, but other indicators which are unaffected by 
this agent are unsuitable for organic acids. 

The possible carbon dioxide error cannot be removed 
by boiling the liquid, since the acid which is almost 
invariably formed by mouth organisms fermenting 
carbohydrates is the inactive ethylidene lactic acid, or 
a-hydroxypropionic acid — 

CH Q — CH 



— and this loses its acid properties upon being heated. 

Except where otherwise stated, the subject of the 
experiments was always the same. 

Lactic Fermentation in Vitro. 

i. Two grammes of each of the following substances 
were taken, mixed by trituration in a pestle and mortar 
with 10 c.c. of distilled water, sterilized, infected with 
0.2 c.c. of mixed saliva, and incubated for four days. 
At the end of this time the acid was estimated, with the 
results as shown in table on p. 201. which are the averages 
of three series of estimations. 

Such an experiment is. of course, wholly in favour of 
the organisms, and it gives the acid production when all 
the substances are under equally favourable conditions, 
which of course would not obtain in the mouth. Some 
would be acted on much more than others by ptyalin 
in the first place before fermentation by the organisms 
occurred, some adhere much more than others to the 
teeth, and some are salivary stimulants, and thus the 
acid formed would tend to be neutralized more in some 
cases than others. It represents, perhaps, the compara- 
tive amounts of acid which would occur in a very " dry " 
mouth, if all the substances tended to lodge equally. 



It is seen that all the carbohydrates form some acid, 
but that there are great differences in the amount 
formed. For instance, from chocolate is formed more 
than twenty times as much acid as from cane-sugar, and 
from parsnips is formed twice as much as from apple. 

As is seen from the second column, these differences do 

Food Material. 

Acid Units : 
C.C. of n NaOH. 

Percentage of Carbo- 
hydrates (Hutchison). 




Malted milk (dry) 





60 «o 



51-0 + 







" Brown " bread 

2-2 5 

48*0 (about) 



8*5 (about) 




White bread 

I-8 7 

5 l, S 




Biscuit (plain) . . 













I '21 








Apple jam 



Raspberry jam . . 


50-0 (about) 

Sugar (cane, lump) 


loco (about) 

n H,S0 4 . 

Fat . . . . . . —0-40 

Ham .. .. .. ; —2*45 


Beef . . . . . . — 2*8o 



not in the least correspond with the amount of carbo- 
hydrate present in each ; but rather it depends upon 
the kind of carbohydrate and its state of comminution. 
It is, too, a very significant fact that all those substances 
from which least acid is produced are the most " sapid " 
substances, and the majority of them (cabbage, potato, 


apple, onion, carrot, apple and raspberry jam) are 
originally acid in reaction. The only materials which 
gave an alkaline reaction were the proteins — the beef. 
ham. and fat. 

As regards the fermentability of the various su- 
Aitchison Robertson* places them in the following order 
: : lactic fermentation: (i) Laevulose ; 2 lacl 
(3) dextrose ; (4) cane-sugar ; (5) maltose. Using 
2 per cent, solutions of the pure sugars infected with 
0*2 c.c. saliva. I obtained the following order : 
ti se; 2 taevnlose maltose; (4) lactose g cane- 

sugar. Both coincide in placing cane-sugar very low, 
and certainly the position of maltose in Aitchison 
Robertson's scale does not hold for the mouth ; for. as we 
shall have occasion to see. and. in fact, have seen for 
Experiment I., maltose (derived from starch) forms 
more acid than almost any other kind : sugar. In 
both larrulose is placed high ; but. again, this does not 
represent practically the amount of acid formed from it 
in the mouth, since those substances which contain 
kevul - except b oey are usually combined with 
salivary stimulants in such a manner as to negative the 
acid production. 

The Effect of Insalivation. 

2. Since certain of the substan ces tested above are 

salivary stimulants and others are not. and some 
require much more mastication and are therefore more 
insalivated than others, and since some are more affected 
than others by ptyalin. it becomes necessary to know 
what is the combined effect of insalivation. mastication, 
and fermentation, on each of the substances. This was 
estimated under the following conditions : The teeth 
were cleaned, and one hour afterwards 2 grammes of the 
substances to be tested were masticated and insalivated, 
until in each case the desire to swallow the mass was felt. 

* Hutchison's " Food and Dietetics," p. 277. 


It was then expectorated into a sterile test-tube and 
incubated for four days ; at the end of which time the 
acidity was estimated as before, with the following 
results. None of the substances were sterilized, and 
each was used in the form in which it is usually eaten. 

Acid Units in Four Day> : 

Food Material. 


. of " XaOH. 



White bread 




" Brown " bread 









2 '5 

Bread and butter, with jam 


Crust of bread 













-4-8 (alkaline) 

The first thing which strikes one in comparing this 
latter list with the former is that several of the sub- 
stances have changed their positions. This, of course, 
is due (1) to the neutralizing effect of the increased 
amount of saliva promoted by some of the substances, 
and (2) to the presence of an increased amount of ptyalin, 
thus converting more starch into maltose. Those 
substances which have taken a higher place in the list 
are those on which the increased ptyalin has acted, 
giving rise more rapidly to a supply of maltose, which 
the organisms have converted into lactic acid. Those 
substances which are lower are so because they have 
induced an extra flow of alkaline saliva, which has been 
sufficient to more than neutralize the increased effect 
of the ptyalin. This may be taken to represent the 
amount of lactic fermentation which would take place 
in any ordinary mouth, provided equal quantities of all 
food substances remained after mastication to be 


fermented. That is to say, supposing a space or spaces 
existed between the teeth in a certain mouth, and which 
were always filled up after each meal, irrespective of 
what composed the meal, then the above table may be 
taken to represent proportionately the amount of acid 
which would be formed from each of the substances, and 
represents for enamels of equal resistance the amount 
of destruction of the surface which would take place. 
It is perfectly clear that the material having the greatest 
potentiality for tooth destruction is starch in a cooked 
and finely divided state. Although, of course, all starch 
must first be converted into maltose before lactic fer- 
mentation can take place, yet it is important to notice 
that much more acid is formed from starch than from 
an equal quantity by weight of maltose in a given time. 
Thus, equal quantities of bread and maltose were 
sterilized and mixed with equal quantities of saliva, and 
incubated for two days. In an average of three tests 
the bread gave 036 acid unit, and the maltose 0-16. 
This is probably due, as Ellenberger and Hoffmeister* 
have suggested, to the more ready t'ermentability of 
maltose in a " nascent " condition. 

Here, then, is amply borne out by experimental proof 
the fact that precisely those articles which form the 
greater bulk of the diet of the higher civilized peoples 
at the present time are those which have the greatest 
potentiality for acid production. Particularly is to be 
noticed the large amount of acid formed by pastry, 
bread (" brown " and white), toast, chocolate, and 
biscuits. Other points of importance are the relatively 
small amount of acid produced from cane-sugar and 
rice. The amount of acid formed from cane-sugar is 
more than in the former table owing to the larger number 
of organisms present, but its position is relatively much 
lower owing to the increased amount of saliva induced 

That so little acid should be produced from rice 

* Archivf. Wissensch. u. Prakt. Thierheilk., Bd. xi., S. 162. 


(boiled) is a little surprising at first, until it is remembered 
what a relatively small surface is exposed to the action 
of the ptyalin and organisms (i.e., the starch is not in a 
finely divided " refined " state). Again, it is noticeable 
that the most sapid substances are responsible for the 
least acid (cf. apple, potato, parsnip, orange, salad, and 
cane-sugar). Bread crust, also, by reason of the 
increased mastication, and therefore salivation, has only 
developed about one-half the acid that the soft white 
bread has. 

Protein material (meat) under these circumstances 
shows a strong alkaline reaction — more alkaline, in fact. 
than the bread was acid ; it might be thought, there- 
fore, that the two might neutralize each other; but, as 
we shall show, this is not so. Ideally, of course, similar 
experiments should be carried out with a person immune 
to caries ; this, unfortunately, has not been possible but 
one substance only, white bread, has been tested in the 
same way with two immune persons. The first gave an 
acidity of i-o, and the second 2-4. both considerably less 
than the figures above. Both of these low acidities are 
due. I think, to the increased neutralization of the acid 
formed, since in both (and especially the first) the 
fluidity of the expectorated mass was marked. 

Fermentation was not complete in any of the sub- 
stances at the end of the four days, since, upon testing, 
they all reduced Fehling. hence showing that sugar 
was still present. Control fermentations tested with 
Uffelmann's reagent showed lactic acid to be always 
present. Occasionally the presence of acetic acid was 
shown by a brown reaction, or /8-hydroxypropionic acid 
by the acidity to litmus remaining after boiling. 

That in a mixture of protein and carbohydrate the 
alkaline decomposition of the one does not neutralize 
the acid fermentation of the other is shown by this 
experiment : Eight mixtures each of bread 1 gramme 
and meat 1 gramme were insalivated and placed in 
sterile tubes : seven were incubated, and one tube 



was examined each day for a week, with results as 
follows : 


Number of Days 

Acid Units developed : 

of Tube. 


C.C. « NaOH. 


after standing one hour 























The acid production obviously increases rapidly up 
to the fourth day ; after that it still increases, but 
more slowly. Any neutralization which might occur 
after the seventh day would be quite valueless,, since by 
that time, as will be shown next, a considerable portion 
of the enamel would have been decalcified. It is seen 
that on the fourth day more acid has been formed 
from the bread and meat mixture than from the bread 
alone (see table on p. 203). This fact has been re- 
peatedly noticed — that the admixture of protein seems 
to increase the rapidity of the acid formation in carbo- 
hydrates. Therefore not only is such a mixture not 
to be regarded as beneficial, but as positively harmful. 

Decalcification of Enamel. 

3. That the order in which the various food materials 
have been placed thus far corresponds to their com- 
parative destructiveness to enamel is supported by the 
following experiment : 

Two grammes of bread, apple, and cane-sugar, were 
each triturated with 10 c.c. of water, sterilized, and 
infected with 0-2 c.c. of mixed saliva. The crown of a 
perfectly sound lower molar tooth (malacotic in type) was 



divided into three equal portions, and a portion placed 
in each of the mixtures and incubated for one week. 
The following table expresses the result : 


Acid Units: 
CC V X OH Condition of Enamel. 


Sugar (cane) 

2*5* Enamel opaque, white all 
over, and quite soft. 

0-6 Slightly opaque at edges 
and on cusp. 

0-4 Very slight opacities near 
edges and cusp. 

The accompanying illustration (Fig. 55) is a photo- 
graph of the three portions of crown after removal from 
the mixtures. The differences in opacity can be readily 
seen. Each portion was scratched with a cross with a 
sharp needle ; the effect is only visible on the portion 
from the bread mixture, and the depth is about 0-5 
millimetre (or about one-fourth of the total thickness 
of the enamel). 

Lodgeability of Foodstuffs. 

4. In the foregoing experiments there is. of course, 
one most important factor which has been entirely 
omitted — the relative tendency of the various materials 
to lodge on or between the teeth. It is a well-known 
fact that certain articles of diet tend to stick to the 
teeth or to leave more debris behind after mastication 
than others. It is perfectly obvious, therefore, that in 
a normally -shaped mouth, if a substance had a high 
acid " potential " but yet did not lodge, it would not be 
anything like so harmful as another substance which 
had a low acid potential, but a great tendency to lodge 
on or between the teeth. The relative " lodgeability " 

* Lower than in the last table because much of the lactic 
acid has combined with the lime salts of the enamel. 


of foodstuffs is therefore a matter of the highest impor- 
tance, and one on which it is necessary to have some 
precise information. After trying several other plans 
for determining this, the following method was adopted : 
The teeth were hrst carefully cleaned with water and 
a tooth-brush ithe form of which will be described 
later). One hour afterwards the substance to be 
tested was eaten for about three minutes in as natural a 

Fig. 55. — Three Portions of the Crown of a Tooth after 
being subjected for one week to the fermentation 
of Bread. Apple, and - from Left to Right 


manner as possible. After the lapse of hve minutes the 
teeth were again cleaned with 10 c.c. of distilled water, 
and the debris carefully collected from the brush in a 
specially - shaped beaker with an inverted rim. In 
order to avoid undue external infection, the brush and 
beaker were previously washed for some minutes with 
alcohol, and the latter allowed to evaporate. 
The actual time of brushing was in each case one 


minute, and care was taken to prevent saliva from enter- 
ing the beaker. The mouth was then rinsed out with 
another 10 c.c. of distilled water, and the whole 20 c.c. 
then incubated in a sterile flask. The period of incubation 
chosen was twenty-four hours, since after this time some 
of the substances which had developed acid were found 
to become alkaline owing to the carbohydrate being all 
used up, and the organisms turning their attention to 
the protein constituents of the saliva. 

The tables on p. 210 give the average results of several 
acid estimations obtained in such a manner. 

These figures may be taken, then, as representing the 
resultant of all the various forces — acid -forming, 
adhesive, neutralizing, and cleansing — at work in the 
mouth. It is the only test which determines practically 
for an " average " mouth the relative harmfulness or 
otherwise of the various articles of diet ; we may there- 
fore say definitely that the order in which the materials 
are placed here represents their relative potential to 
initiate caries of the teeth, with the exceptions that 
lemon is probably more beneficial and cane-sugar more 
harmful than these tables show. 

All the materials in the first table have a potential for 
causing caries ; all those in the second table have either 
no such tendency or one which is very readily neutralized. 
The lodgeabilily of the various materials evidently does 
not depend upon the amount of fibrous or inert matter 
they contain. As is shown by the second column, the 
amount of acid or alkali formation bears no proportion 
to the amount of cellulose contained in the material. 
Compare, for instance, orange and brown bread ; both 
contain the same amount of cellulose, yet the former 
gives an alkaline reaction of 0-5, and the latter an acid 
reaction of 0-4 ; and figs, with 73 per cent, of cellulose, 
result in an acid reaction, whilst bananas, with only 
-2 per cent. , have an alkaline result. Several substances, 
too, with no cellulose at all yield less acid than those 
with a moderate amount. It is evident, therefore, 



that some other explanation must be sought to account 
for the variations. 

There is one property which sharply differentiates these 
two series of foodstuffs. It is their acidity, or alkalinity. 

Acid Units 

Cellulose per 

Food Material. 

as C.C. 


N NaOH. 














" Brown " bread 






White bread 









'Peppermint (containing glucose) . 






Bread and honey 






Cane-sugar 10 per cent, in water . 






Alkalinity as C.C 

Cellulose per 

Food Material. 

N H0SO4. 



— O'lO 


Lemon . . 



Parsnip . . 

- 0'20 



- 0'22 


Banana . . 

. ' -0»25 








Orange . . 

- -50 


Meat (beef) 

- 0-50 



- 0-87 


- i-8o 

All the substances which are in the first table, and 
therefore harmful, are originally either alkaline or neutral 
in reaction ; all the carbohydrate substances (with the 
exception of nuts) in the second table, and therefore 
beneficial, are originally acid in reaction. In other words 


and in general terms, salivary depressants tend to lodge 
and remain in the mouth more than salivary excitants. 
Two series of the same substances similarly treated were 
also incubated for four and eight days in order to deter- 
mine how long it took the organisms to use up the 
carbohydrate in the several instances. At the end of four 
days the substances which showed acid reaction were — 

Pastry. Biscuit. 

Toast. Crust of bread. 

Chocolate. Cane-sugar. 

At the end of eight days the only substance which 
remained acid was cane-sugar ; white bread was neutral, 
all the remainder being strongly alkaline. 

Here again it is seen that six of the most common 
articles of our modern dietary are the ones which give 
rise to the most prolonged acid reaction in the mouth. 

The position of cane-sugar is hereby completely 
reversed, and from an apparently harmless form of carbo- 
hydrate it becomes (in this form, at least) equal to the 
most harmful ones, owing to its prolonged action. The 
reason for this difference of behaviour of cane-sugar in 
vitro and in the mouth is to be found in the fact that this 
substance is. as has been shown, a powerful excitant of 
the mucous glands of the mouth. The resulting viscid 
mucin binds the sugar to the teeth, and, not being acted 
upon by ptyalin, it remains and is slowly fermented by 
the organisms alone. 


The question which now arises is, Can we by a 
combination or sequence of salivary depressants and 
excitants reduce the fermentable debris remaining in 
the mouth* after a meal ? 

* " In the mouth," and not in apposition to the teeth alone, 
since the debris which remains in the buccal sulcus, for instance, 
forms lactic acid, and this, combining with alkaline salts of the 
saliva, considerably reduces its power of neutralizing the acid 
formed near the teeth ; particularly does this apply to parotid 
saliva and its already somewhat feeble protective properties. 


To consider first of all a sequence. Substances which 
were known to produce most acid were eaten, and then 
followed immediately by other substances which had 
been shown to result in an alkaline reaction. The teeth 
were then brushed and the mouth rinsed, and the 
washings incubated as before, with the following results : 


Bread and butter followed by apple . 
Bread and butter followed by orange 
Bread followed by radish 
Bread followed by fish 
Bread followed by duck 
Rice followed by orange 
Chocolate followed by apple 
Cake followed by orange 
Bread and butter and caramels followed by 
kauri-gum (chewed)* 









Here, then, is an important fact, that by such a 
sequence the deleterious effects of acid-forming sub- 
stances can be completely overcome, and an acid result 
transformed into a neutral or alkaline one. This, 
obviously, is of the utmost importance as a physiological 
means for the prevention of caries, and offers a most 
simple and efficacious method whereby the commencement 
of the process of decay may be obviated. 

The method would probably not be equally efficacious 
if carious cavities were already present and unfilled ; 
it could not, however, be other than beneficial ; but 
this aspect does not immediately concern us. Given a 
mouth in which the teeth are fairly regular and in which 
there are no gross cavities to retain the previously eaten 
soft fermentable food, then we may with /safety say 
that, if such food be followed by articles of " alkaline 
potential " and salivary excitants, the tendency to 
caries will be enormously reduced or entirely negatived. 
I see no reason whatever why such a sequence should 

* This substance was chewed extensively by the Maoris, and 
was probably a factor in producing their remarkable freedom from 



not always, and at every meal, be practicable ; but in 
case it should not be so. we consider the next question : 

Can we by the use of a combination of such sub- 
stances attain the same results ? 

The following table, being the results of estimations 
made in a similar manner to the above, but the sub- 
stance being mixed and not in sequence, supplies an 
answer : 

Acid or Alkaline Units : 
Substance. n NaOH and H 2 S0 4 

in 24 Hours. 

Bread and butter with raspberry jam . . . . 0*5 acid. 

Bread and meat mixed . . . . . . . . 0*3 ,, 

Bread and butter with melon jam (containing 

lemon and ginger) . . . . . . . . 0*2 „ 

Bread and butter with marmalade (sweet) . . 0*2 ,, 

Cake with 30 per cent, of bran added . . . . o«i 

Bread and butter with quinine, 1 in 800 . . 0-3 ,, 

Bread and butter with acid potassium tartrate Neutral. 
Bread and butter with acid postassium tartrate 

and o-oi per cent, saccharine . . . . . . ,, 

Biscuit with tartaric acid 1 per cent. . . . . ,, 

Bread and butter with tartaric acid 1 per cent. 0*08 (alkaline). 

Cane-sugar with tartaric acid 1 per cent. . . 0*05 

Cane-sugar with lemon-juice .. .. .. 0*15 

In this case the results are not as marked. It is 
obvious that a more powerful salivary stimulant must 
be mixed with the bread in order to reduce its lodge- 
ability, and therefore its acid production. 

It will be noticed that raspberry jam had the effect of 
increasing the acid production, whilst " melon " jam 
slightly reduced it. Quinine had practically no effect 
at all. Only tartaric acid and its potassium salt were 
sufficient to prevent acid production. 

The fact of rendering a substance very fibrous by the 
addition of bran, although reducing the acid production 
somewhat, does not prevent it, and is nothing like so 
efficacious as the acids. The mixture of meat with 
bread likewise has very little effect, only reducing the 
acidity from 0-35 to 0*3, but since the meat probably 
exercised a certain detergent effect, this amount of acid 


has been formed from a very much smaller quantity of 
bread. This was quite obvious from a naked eye 
examination of the " washings." With regard to 
" sugar." we now observe what is a most important 
principle — i.e., that by its combination with an acid its 
lodgeability and " acid potential " are not only nega- 
tived, but for the first time we get an alkaline result. 
This is to be accounted for by the fact that the acid pre- 
cipitates the mucin, and therefore it no longer has the 
power to bind the sugar to the teeth ; the resulting extra 
flow of a thin alkaline saliva washes the sugar clear of 
the teeth, and leaves only an alkaline deposit, or one 
which, on decomposition, yields alkaline substances. 

A similar explanation accounts, of course, for the 
alkaline result from the bread, but in this case the 
mucin factor is not present — at least, to anything like 
the same extent. 

It has been insisted upon always by physiologists that 
sugar is a valuable food, and therefore an article of diet 
to be recommended ; but dental practitioners have 
always equally insisted that the consumption of sugar 
was a potent factor in the production of caries, and one, 
therefore, to be avoided. Here. then, we have a means 
of giving sugar — by combining it with an acid — which 
will not only not be harmful to the teeth, but actually 
beneficial, since the combination of sugar and acids 
promotes a profuse after-flow of alkaline saliva. 

We have previously seen that the fact of diluting the 
sugar largely with water (90 per cent.) does not prevent 
acid production. There is, therefore, only this means 
whereby sugar may be prescribed harmlessly. 

It is to be noted that it is in this combination 
that sugar is most commonly provided by Nature — i.e., 
combined with the acids or acid salts in roots, plants, 
or fruit. It is therefore a condition which should always 
be enjoined when advising the consumption of sugar as 
a food, especially in regard to children. 



1. That as to their fermentability and lodgeability — 
the "acid potential" — -all carbohydrate articles of diet 
fall into two well-defined groups : 

(a) Those of originally neutral or alkaline reaction, 
giving rise to the formation of much acid. 

(b) Those of originally acid reaction, giving rise to 
very little or no acid, or a definite alkaline reaction. 

2. That by a mixture of strong salivary stimulants 
with the acid - forming carbohydrates the resulting 
reaction may be turned from an acid to an alkaline one. 

3. That this latter effect may be more certainly 
obtained by a sequence than by a mixture. 

4. That a mixture of protein (as meat) with carbo- 
hydrate has practically no effect in reducing the amount 
of acid formed, but that a sequence of meat after carbo- 
hydrate does prevent the formation of acid, probably 
by its detergent action. Such a sequence is, however, 
quite impracticable and undesirable, and therefore has 
not been considered. 


That in order to prevent the retention of fermentable 
carbohydrates on and between the teeth, and so elim- 
inate or very considerably reduce the carbohydrate 
factor in the production of caries, starches and sugars 
should on no account ever be eaten alone, but should in 
all cases either be combined with a substance having a 
distinctly acid taste, or they should be followed by such 
substances as have been shown to have an " alkaline 
potential "; and the best of these are, undoubtedly, the 
natural organic acids found in fruits and vegetables. 




The Use of Antiseptics. 

Ever since the role which bacteria play in the pro- 
duction of caries has been recognized, antiseptic dings 
have been widely used in the prophylactic treatment of 
the disease, both by the laity in proprietary articles and 
in the prescriptions of medical and dental practitioners. 
This use has been more or less empirical, or, rather, based 
upon the general principle that where organisms are, 
there of necessity antiseptics should be also, in order to 
maintain the health of the tissues. 

I do not think it has ever been claimed by anyone 
that from clinical experience any good whatever has 
been seen to accrue from their use. It cannot be said 
that they have checked or arrested the progress of caries 
in the slightest degree. The mouth is an extremely 
difficult cavity to deal with by means of antiseptics. 
When we remember how extremely difficult it is to 
sterilize the hands even, the whole surface of which can 
be well scrubbed for a prolonged time, and can be im- 
mersed in antiseptics of far greater strength than could 
be tolerated in the mouth, we can realize how extremely 
difficult, if not impossible, it must be to obtain a con- 
dition approaching sterility in the mouth. It is a 
cavity made up of nooks, corners, folds, and irregu- 
larities, every angle and surface of which is coated with 
micro-organisms; and, as is well known, such conditions 
offer great obstacles to the action of antiseptics, and 



favour the development of bacteria. (Even with the 
utmost aseptic precautions, using a sterile cannula and 
segregator, I have found it practically impossible to 
get a sample of saliva free from organisms.) 

The cavity is one, too, which is always moist with an 
albuminous and alkaline fluid, and this tends in the 
majority of cases to at once combine chemically with 
the antiseptic and render it innocuous (the potent 
antiseptics being chiefly the salts of heavy metals). The 
majority of such antiseptics, too, at once check the 
action of ptyalin. Moreover, when it is remembered 
how comparatively infinitesimal is the length of time 
during which such antiseptics are used, it would be 
surprising indeed if any beneficial action were to result. 
The time, as a rule, spent in rinsing the mouth is rarely 
more than, if as much as, a minute. Supposing this be 
done three times a day. this makes three minutes in 
twenty-four hours, or for every minute the antiseptic is 
acting there are 1437 during which it is not acting ; 
and bearing in mind the rapidity with which organisms 
proliferate, it does not seem at all likely that such a 
short and partial exposure to an antiseptic would result 
in any permanent lowering of the number of organisms 
in the mouth. 

Certainly the use of antiseptics is not based upon the 
findings of any scientific investigations. 

R. Bessenge* has tested the antiseptic value of a 
large number of mouth-washes, and concludes that 
hydrogen dioxide 10 per cent, alone acted antiseptically 
in a few seconds ; all the remainder required at least 
four minutes — a length of time which would be im- 
practicable to recommend for the routine use of mouth- 

Wadsworth.t after testing a number of antiseptic 
mouth-washes, such as formalin, lysol, hydrogen dioxide, 
found that none were so efficient as alcohol 30 per 

* Deutsche Medizinische Wochenschrift, August 19, 1909. 
f Journal of Infectious Diseases, October 30, 1906. 


cent., preferably with glycerine and sodium chloride 

Against this supposed beneficial action of alcohol, 
however, are the findings of Floxas,* who, after the 
examination of 729 workmen, found that the percentage 
of caries in total abstainers was nearly one-third less 
than in those who took alcohol, the ratio being remark- 
ably constant for all ages from fifteen to fifty. Prob- 
ably, too, the amount of alcohol taken into the mouth, 
and the total length of time the oral tissues were bathed 
in alcohol per diem in the case of those who habitually 
drank alcohol, would be far in excess of the amount and 
time which any person would devote to the use of an 
alcoholic mouth-wash each day. Since the subjects of 
the investigations were, however. Mohammedans, it is 
probable that those who were not faithful to the 
Prophet's teaching indulged in alcohol to excess, and 
thus produced a vitiated condition of the gustatory 
nerves, leading to a decreased salivary secretion. 

Huntf has investigated the inhibitory effect of a 
number of antiseptics used as mouth-washes. The solu- 
tions were used in the mouth for one minute, and 
cultures were taken from mixed saliva five minutes, and 
also one hour, afterwards ; these were plated out, and~ 
the number of colonies counted. It is to be regretted 
that no control cultures were made — i.e., cultures before 
the use of the solution — so that the actual diminution 
in each case might be known. However, none of the 
solutions used produced anything like sterility of the 
mouth even for five minutes. This coincides with my 
own observations on the subject. I have on several 
occasions tested the antiseptic values of mercuric 
chloride, formalin, and hydrogen peroxide, in such 
strengths as could be tolerated in the mouth without 
discomfort, and also various proprietary lozenges said 
to contain formic aldehyde ; and none of them, even 

* Dental Cosmos, 19 10, p. 939. 
f Ibid., October, 1904, p. 818. 


when used vigorously with the tooth-brush, were 
capable of producing anything approaching an aseptic 
condition of the mouth even for five minutes — when the 
cultures were taken. The colonies were not counted, 
but thymol was added to each after twenty-four hours, 
and the turbidity of the broth compared. The only 
ones which showed any marked lessening of turbidity 
as compared with their controls were mercuric chloride, 
1 in 2,000, in a culture taken one minute afterwards, 
and the hydrogen peroxide — five minutes. The mer- 
curic chloride five-minutes culture showed a turbidity 
only just appreciably less than the control. 
The following are the averages of Hunt's results : 

Number of 

Organisms in 

£ C.C. Saliva after 

Five Minutes. 

Number of Organisms in 


}■ C.C. Saliva after 
One Hour. 

Formalin, 1 : 200 


1,590,000= X 2-^, 

Benzoic acid, 1 : 200 


no,5i4=x 5*5 

Salicylic acid, 1 : 200 


640,616= x 3-0 

Mercuric chloride, 1 : 3,500 

20,1 15 

333,180= x 16-0 

Mercuric chloride, 1 12,500 


5,752=x 1-5 

Mercuric chloride, 1 : 2,500 

(with a number of other 

ingredients — thymol, 

menthol, alcohol, and 



2,458 = -=- i-i 

From this it would appear that the only antiseptic of 
any material value in the reduction of the number of 
organisms in the mouth is mercuric chloride, and 
this only when combined with a number of other sub- 
stances. The antiseptic value of the other ingredients 
does not seem to have been tested, so that the prolonged 
action seen in this case alone may have been due to their 
use, and not to the mercury. 

Miller tested the antiseptic action of a number of 
drugs used as mouth-washes. His conclusions are all 
based on the time taken by the particular antiseptic 


to devitalize mouth organisms in vitro ; and this being 
so, the results are not of much practical value, since 
the conditions in the mouth are so totally different. 
Everything in the mouth is in favour of the organisms ; 
in vitro everything is in favour of the antiseptic ; and 
although a drug destroyed all the organisms in a test- 
tube in one minute, it is obvious from preceding remarks 
that to infer anything like a similar action in the mouth 
would be extremely fallacious. 

There are, too, several very strong objections to the 
use of the more powerful antiseptics as mouth-washes : 

i. Many of them are extremely poisonous. Miller 
and Hunt have both pointed out that the risk of swallow- 
ing sufficient to cause toxic symptoms is very remote, 
and doubtless this is so in adults of average intelligence. 
It is not, however, with adults so much that we are con- 
cerned in the prevention of dental caries — it is with 
children ; and it is not always possible for someone to 
supervise the cleaning of the teeth, so that there would 
be great danger of too much being swallowed, as anyone 
who has watched children cleaning their teeth and 
washing their mouths out will know. 

2. Chassevant and Richet* have shown that in the 
process of lactic acid fermentation the addition of metallic 
salts in very slight degrees of concentration, although 
having an inhibitory effect upon the micro-organisms, 
may not interfere with the acid production at all. My 
own experience supports this. For instance, if carbo- 
hydrate be infected with mouth organisms and lactic 
acid formed, and if this be then neutralized and strong 
thvmol solution added, the carbohydrate will slowly again 
become acid, although subcultures show the process to be 
a sterile one. That is to say, the antiseptic has destroyed 
the organisms, but not their enzymes. 

3. Lastly, and most serious objection of all, most of 
the stronger antiseptics are salivary depressants, and 
hence, by diminishing the flow of saliva, they promote 

* Comptes Rendus, cxvii., p. 673. 


stagnation in the oral cavity, remove the natural means 
of protection, both active and passive, and hence make 
conditions much more favourable for the organisms. 
Hunt in his investigations noted this point, but did not 
attach any importance to it. He says that after using 
the antiseptic mouth-wash it was ejected, and " the 
variation in amount between it and the wash taken 
into the mouth was too small to measure with a 
graduate." This means, of course that during the 
minute which the antiseptic was in the mouth no flow 
of saliva had occurred. The use of such drugs, there- 
fore, undoubtedly in this respect alone more than coun- 
teracts any beneficial action they may have as disin- 
fectants, and, if habitually used, may do far more harm 
than good. 

Note. — The above only relates to antiseptics used 
for the prevention of caries. Undoubtedly, in acute 
inflammatory conditions of the mouth antiseptics are 
indicated and necessary ; their usefulness, though, is 
increased by being used in conjunction with salivary 

The Use of the Tooth-Brush. 

That the teeth may remain perfectly healthy without 
the use of a tooth-brush is evidenced in the case of 
many " native " races, and also in isolated cases in 
higher civilized races. On the other hand, many un- 
civilized peoples assiduously clean their teeth with a 
pointed stick frayed out at the end, and it is noticeable 
that this occurs in those races whose normal diet is 
less acid and softer than that of others — i.e., Kaffirs and 
some Hindus. 

The food of modern civilized peoples is essentially 
soft and little acid ; and since it has been shown that such 
foodstuffs not only adhere more to the teeth and pro- 
duce more acid, but also fail to evoke the " natural " 
agencies of protection (since they are not " natural " 


stimuli), it would seem only reasonable that some arti- 
ficial means should be adopted to promote the more 
rapid removal of such debris from the teeth. 

That by means of the tooth-brush a considerable 
amount of fermentable material may be removed from 
the teeth is proved by the experiments on the relative 
lodgeability of various foodstuffs. Even if, as is quite 
possible, all the debris is not thus removed, it is obvious 
that it must considerably reduce the amount capable 
of being transformed into acid, and so enable the saliva 
to deal with the remainder. 

The following experiments bear on the question : 

i. The teeth being unbrushed for twenty-four hours, 
bread was eaten, and five minutes afterwards the 
debris was collected by brushing the teeth, and incu- 
bated in the manner previously described. In twenty- 
four hours 0-3 (\J) units of acid were developed. Half 
an hour after the brushing bread was again eaten, and 
the debris collected and incubated. At the end of twenty- 
four hours only 0-15 acid units had developed. 

2. The teeth being uncleaned for twenty-four hours, 
bread debris was collected in the usual way, and neutral 
litmus added. In two hours it became distinctly acid. 
The same procedure was carried out a few minutes after 
cleaning the teeth, and the incubated debris did not 
become acid for five hours. 

Other experiments were confirmatory of these results. 
We may therefore assume — (a) That the tooth-brush 
does remove a considerable amount of acid-forming 
debris ; (b) that the tendency for certain foods to lodge 
on brushed teeth is less than on unbrushed teeth, since 
the total amount of acid formed was only half in the 
former case what it was in the second, and the time 
required to become acid was more than double. 

The form of tooth-brush generally used, and the 
manner of using it, as a rule leave much to be desired. 
The brush must be a small one ; the bristles should be 
neither too hard nor too 50ft, and should be of unequal 


lengths ; the handle should preferably be bent at an 
obtuse angle away from the bristles. Such a brush is 
shown in Fig. 56. With such a brush all surfaces of 
the teeth can be reached, and only about two teeth can 
be brushed at the same time. This is a very essential 
point, since it necessitates 
a little longer time being 
spent on the operation. 
But most important of all 
is the manner of brushing. 
As a rule teeth are not 
brushed ; they are rubbed 
and scrubbed. Food de- 
bris is simply forced into 
the interdental spaces. 
and the inibrieations of the 
enamel are likewise filled 
up. The error arises 
through a non-apprecia- 
tion of conditions and 
structure. Let a person 
thoroughly grasp the fact 
that the surface of a 
tooth is not smooth, but 
" rough " or corrugated ; 
that it is coyered by a 
tough membrane ; that 
what it is required to 
remove has not soaked 
into the teeth, but is 
lying against them, and 

he will naturally and Fig. 56.— Tooth-brush. 

unconsciously adopt the 

right kind of action — i.e., he will brush the teeth. To 
give a homely simile, the teeth should be brushed after 
the manner that a clothes-brush is used, rather than as 
a >: rubbing-brush is.i Such brushing is only possible 
with a very small brush. The name " tooth-brush " as 


applied to articles long enough to reach from the canine 
tooth to the last molar is a misnomer ; there is not 
possibly enough room in the mouth for their use in 
" brushing." The more prominent parts of the teeth 
only can be scrubbed, and by no means can the food 
debris be brushed off the teeth as it should be. 

Instructions, then, should be given to brush the teeth 
systematically. The mouth should be held wide open, 
and a commencement made at the last molar of one jaw, 
the brush coming forward to the canine region, then re- 
turning along the opposing teeth. Next, the other side is 
treated similarly, and lastly the incisors. Not more than 
two teeth at a time should be brushed, and this should 
be done both horizontally and vertically (away from the 
gums) for the buccal and labial aspects, and forwards 
and sideways for the occlusal surfaces. Such instruc- 
tion may sound rather tedious, but in practice it is 
exceedingly simple ; the habit is soon acquired, and the 
total time, including several cleansings of the bristles, 
need not exceed two or three minutes. (This likewise 
sounds a very short time, but it will seem a rather long 
one to many people.) 

It is obvious that under modern conditions of life the 
tooth-brush cannot be relied upon alone to prevent 
caries. If it could be used assiduously, and in the 
manner described, immediately after every meal, this 
might be so, but in the vast majority of cases such a 
suggestion would be impracticable. 

Ihe tooth-brush should rather be regarded as an 
adjuvant to other means of prophylaxis ; and if, as 
is most frequently the case, it is used only in the 
morning, as something which will lessen the ten- 
dency of foodstuffs to lodge against and between the 

The brush should, of course, be kept clean, either by 
permanent immersion in a weak antiseptic solution or 
by being washed daily with soap and water. 

D. D. Smith of Philadelphia has of recent years 


elaborated what may be termed the apotheosis of 
mechanical prophylaxis. Patients are required to 
present themselves at least once a month, when each 
tooth is individually subjected to a vigorous cleansing 
and polishing on every surface by the use of wood 
points and pumice. The results are said to be excellent. 
This is doubtless brought about by the decreased 
tendency of foodstuffs to lodge on highly polished 
surfaces. Smith claims that the mechanical stimulus 
brings about a reaction on the part of the pulp, causing 
solidification of the dentine and enamel, but, so far as I 
know, has not attempted to show how lime salts may 
pass from the pulp to the enamel surface ; and any 
solidification of the dentine is absolutely immaterial. 
In fact, according to the views which we have advanced 
as to the post-eruption hardening of enamel, Smith's 
treatment would probably prevent such action taking 

The method may be regarded as one which may pre- 
vent dental caries, but as one which is extremely limited 
in its application. Probably not 1 per cent, of those 
afflicted with caries could afford it; and, as Miller has 
pointed out, those who do submit to it are patients who 
would otherwise be very careful in their attention to the 
teeth at home. 

Another school — those dentists practising what are 
known as Black Club methods — are enthusiastic advo- 
cates of the prevention of caries by the excision of all 
vulnerable areas in susceptible teeth and replacing them 
with gold — a method which, if followed to its logical 
conclusion, should lead to the gold encasement of half 
the teeth of civilized peoples. To say that because 
caries has attacked one spot in the surface of a tooth, 
therefore the total destruction of that surface is inevit- 
able unless the whole of it is excised, is merely a confession 
of failure to be able to prevent caries by rational or 
physiological means. 



The Use of Dentifrices. 

It has been shown previously that the great majority 
of dentifrices are salivary depressants, in that they are 
composed chiefly of chalk, and therefore alkaline in 
reaction. Undoubtedly the majority of dentifrices are 
far more strongly alkaline than is saliva, and if they 
did not interfere with the salivary secretion their use 
could not be other than beneficial ; but this is not so. 
What occurs is that the mouth for a minute a day is 
rendered highly alkaline, but this is brought about at 
the expense of lessening the amount and alkalinity of a 
constantly flowing natural mouth-wash ; and there can 
be no doubt that for the purpose of neutralizing acids 
which are slowly but continuously being formed a con- 
tinuous alkaline flow is much more efficacious than the 
application of a comparatively strong alkali for about 
one minute, or at most two, in twenty-four hours. We 
are therefore driven to the inevitable conclusion that 
alkaline dentifrices and mouth-washes for the prevention 
of dental caries must be abandoned, and we further con- 
clude that some substance which is a salivary stimulant 
should be used in order to promote and educate the 
activity of the salivary glands. Now, it has been also 
conclusively proved that the best substances for this 
purpose are acids, and there is not the slightest reason 
why the best should not be used in this case. 

The objection will probably be at once raised that 
acids are " bad for the teeth," in that they can be shown 
to decalcify them ; this is one of the fallacies of experi- 
ments conducted entirely in vitro. It has been shown 
that comparatively weak acids are the best salivary 
stimulants, even though they should cause some super- 
ficial decalcification, which it will be shown they would 
not ; but even if they did, and at the same time pre- 
vented caries from occurring, it would be infinitely the 
lesser of the two evils. -"The evil would be manifested 
probably as erosion, attrition, and abrasion; but these 


would be slow in progress, infinitely less in prevalence; 
and, moreover, the children would escape, which is the 
very gist of the problem with which we are dealing. 
But would acids cause any decalcification when used in 
this way ? We have already seen that five and fifteen 
minutes after their use the alkalinity index of the mouth is 
always considerably increased above normal, and that in 
the case of as strong an acid as citric in the lemon, two 
minutes after its use. and including small fragments of 
lemon, the saliva was intensely alkaline. This mav be 
readily tested roughly by anyone with a piece of litmus- 
paper placed in the mouth or against the teeth half a 
minute after eating or washing the mouth out with any- 
thing weakly acid. Undoubtedly, there is a short time 
during which the acid remains unneutralized, but this 
is not sufficient to cause any effect, except, perhaps, on 
the occlusal surfaces in the case of masticating acid 
substances which are actively pressed and ground 
between these surfaces. 

From a very large number of observations, I am con- 
vinced that no harm will accrue to the teeth from the 
use of. those acids, in such strengths as they are active 
salivary stimulants. An acid substance which it is 
suggested should be used in a general manner for this 
purpose is acid potassium tartrate. This substance has 
several advantages : 

1. It is an active salivary stimulant. 

2. It is a form of acid which is widely distributed 
in Nature, and one, therefore, to which the saliva rv 
glands have by the process of evolution been adapted. 

3. Its solubility is only 1 in 200 of water, and, therefore, 
if it be used in the liquid form there can be no danger of 
its being used in too strong a solution, either on account 
of faulty making-up or of subsequent evaporation. 

4. It has an agreeable taste, which may be made more 
so by the addition of saccharine. This is, again, an 
extremely important factor in applying these principles 
to children. 


In the laboratory, sclerotic and malacotic teeth have 
been actively scrubbed daily for a period of six months 
with a saturated solution of acid potassium tartrate, 
without in any case producing the slightest sign of any 
decalcification, or abrasion even. The teeth after the 
scrubbing were kept in water at about neutral point, 
whereas in the mouth they would have been immediately 
bathed in a much stronger alkaline fluid. 

We have already shown, too, how the addition of this 
salt to saliva is beneficial in precipitating the mucin and 
in favouring dialysis. Its addition to saliva causes the 
latter to become watery, and well adapted to flowing and 
percolating between the teeth and into fissures and 
grooves ; whereas the addition of a similar amount of 
carbonate of soda causes the saliva to become thick and 
viscid, and eminently unsuited for its function — in fact, 
promotes stagnation instead of circulation. Moreover, 
should any acid potassium tartrate remain in the saliva, 
it seems to undergo an alkaline decomposition. For 
instance, 2 c.c. of saliva made faintly acid by the addi- 
tion of this salt were incubated ; in twelve hours it was 
faintly alkaline, and in forty-eight hours it showed an 
alkalinity of ro (- N q)- Again, to 10 c.c. of a mixture of 
glucose and saliva, acid potassium tartrate was added 
until it showed an acidity of 5 units per c.c. It was 
then incubated for two days, when the acid units present 
were found to be only 0-22 per c.c. This rapid reduction 
of its acidity in the presence of mouth organisms has 
been repeatedly observed; so that, in the extremely 
unlikely case of any remaining in the mouth unneutral- 
ized, it would become progressively less acid, and finally 
alkaline. Such a mouth-wash as has been indicated 
should be used to rinse the mouth thoroughly in the 
first place. The teeth should then be brushed. It is 
sufficient in the case of children to use the tooth-brush 
with water alone, then to rinse the mouth again thor- 
oughly with the acid-sweet wash ; this will cause a rapid 
secretion of alkaline saliva, which should be, by the 


action of the cheeks, tongue, and closed lips, forced 
through the dental interstices. The mouth should 
always be rinsed out in this fashion both before and 
after brushing, in order to clear the approximal surfaces 
of the teeth ; this is facilitated by the presence and direc- 
tion of the imbrications on the surface of the enamel, 
guiding and directing fluid in horizontal channels 
between the teeth, whereas their presence actually 
hinders the use of a tooth-brush, since the latter can in 
this situation only be used in a vertical direction — i.e., 
at right angles to the imbrications. Floss silk would 
be an excellent material for clearing the imbrications 
if it could be used, but in the majority of cases it cannot 
be, on account of the difficulty of passing it between 
the teeth ; this material is, I think, to be regarded as 
indicated only in quite special cases. 

The following are examples of formulae which may be 
employed as acid mouth-washes : 

A. R Potass, tart. ac. 

Sodii chloridi 



B. R Potass, tart. ac. 

Ac. tartarici 



C. R Ac. tartarici 

Quin. sulph. 



D. R Potass, tart. ac. 

Ac. tartarici 
Ol. limonis 

Of the above, the last (D) is the most pleasant com- 
bination, and the one containing quinine least so ; the 
first one (A) possesses a bland and soothing effect, and 
would probably be efficacious in catarrhal conditions of 
the mucous membrane. These formulae are only sug- 


. 11, 










, i. 


4 • 








i • 










4 • 





gestions. and may be modified in various directions to 
suit special cases or " tastes." The saccharine (glu- 
sidum) and the tartaric acid may in some instances, 
perhaps, be reduced by one-half. In order to ascertain 
the action and effect of such mouth-washes, the above 
series was tested in the following manner : The acidity 
of 10 c.c. of the solution was first estimated in terms of 
^o NaOH ; the mouth was then washed out for one 
minute with io c.c. of solution, and the amount expec- 
torated was measured. Five minutes afterwards the 
" resting " saliva was estimated for amount and alka- 
linity per minute. The results are expressed in the 
following table : 

Variations produced in the 

Resting Saliva Five Minutes 
after using Mouth-Wash. 


Acidity of 


Acidity Amount 
on Expec- expector- 
toration. atedinC.C. 

C.C. per Alkalinity 
Minute, per C.C. 









o'40 12*0 
no 12*6 
130 13'0 
0*65 14*0 

2' 5 I'OO 

2*4 i'o6 
27 1*24 

2*9 1*28 


It is therefore clear that the acidity of such solutions 
is rapidly diminished whilst being used, and that they 
subsequently give rise to a very much increased alka- 
linity index. One minute is possibly longer than they 
would be retained in the mouth in actual use, and prob- 
ably two half-minutes with an interval between would 
be more efficacious. 

It will be noticed that in all cases the amount of fluid 
expectorated was greater than that taken in. showing 
an increase of from 2 to 4 c.c. — that is to say that during 
the minute that the solution was in the mouth salivary 
secretion was actively going on. This is in striking con- 
trast to what Hunt found during the use of antiseptics 


(see p. 221). As a control, distilled water was tested in 
a similar manner, and in all cases the amount of fluid 
in the mouth became less ; this is a curious phenomenon 
which I do not think has been observed before,, and is 
probably due to osmosis, the water passing into the 
cells of the mucous membrane of the mouth. Several 
individuals have been tested on several occasions, and 
always with the same result, the diminution varying 
from 1 to 3 c.c. This would seem to suggest that when 
it is required to obtain the full therapeutic effect of a 
drug on the oral mucous membrane, it should be in such 
strength that the solution will have a lower endosmotic 
equivalent than saliva. 

The use of the mouth-wash will, of course, be most 
efficacious at night-time, since it will not only remove 
the greater part of the carbohydrate debris from the 
mouth, but will promote an increased secretion of saliva 
with strong alkaline and diastatic properties, which will 
be more than sufficient to deal with any carbohydrate 
remainder before the organisms have the opportunity 
during the night of converting it into acid. 

In cases where there would appear to be a tendency 
to rapid caries, the use of such a mouth-wash should be 
insisted on at least three times a day. If the extreme 
seriousness of the condition be explained to parents, 
there will be no more difficulty about this than in en- 
forcing the " taking of medicine " during the course of 
any other disease ; in fact, there will be considerably 
less difficulty, since it is very pleasant to the taste. (I 
have found that for this reason, as a general rule, chil- 
dren are more keen to remember its use than are their 
parents.) The swallowing of such solutions is. moreover, 
not at all harmful, and may be beneficial.* 

In the cases of adults, especially where there is any 
tendency to staining of the teeth or the deposit of cal- 

* On the contrary, the constant swallowing of chalk from 
alkaline dentifrices may very possibly be a cause of chronic 


cuius, acid potassium tartrate in the form of a tine 
powder may be used on the brush very occasionally. 
provided that the teeth are brushed and not scrubbed, 
or. no doubt, marked abrasion might soon result. The 
use of the solid salt also is immediately followed bv a 
rapid secretion of saliva, which should likewise be forced 
through the dental interstices. 

Of course, other acids or acid salts may possibly be 
used in a similar manner. There are. however, two 
dangers to be guarded against- — those of using an acid 
either too weak or too strong. If an acid be used in too 
weak a solution, it will certainly do much more harm 
than good, for it will reduce the alkalinity of the mouth 
without exciting any increased flow of saliva, and thus 
for some time the reaction of the mouth may be actually 
acid ; or the weak ac'd. by being unneutralized too long, 
may in a stagnating cavity attack the enamel of the 
teeth itself. This is evidently why the lactic acid of 
fermentation is not neutralized — it is formed in such 
small quantities that the gustatory nerves are not 
stimulated. If an acid be used in too strong solution, 
it may have a precisely similar effect : the stimulus to 
the gustatory nerves will be too great ; A will have a 
paralyzing effect, and the flow of saliva be consequently 
diminished, giving the opportunity to the stronger acid 
to directly attack the teeth. 

Acid mouth-washes will also, I think, prove to be 
beneficial in reducing the number of acid-forming 
organisms in the mouth ; for. as is well known, those 
organisms which form acid are very sensitive to the 
action of acids.* Moreover, all organisms are very 
sensitive to sudden changes in the composition and 
specific gravity of the media in which they are growing, 
and such changes are brought about in the saliva by the 
action of weak organic acids. 

The use of such mouth-washes will also tend to keep 

* Oppenheimer : "Ferments and their Action," p. 237 
Cohn : Zeitschrift f. Physiol. Ckemie, adv. j- : . 


the calcium phosphate and carbonate in solution, instead 
of their being precipitated upon the teeth in the form 
of calculus, which, as is well known, sooner or later leads 
to a serious condition of oral sepsis. On the other hand, 
the use of chalk dentifrices frequently promotes the 
formation of calculus by particles remaining against the 
teeth and acting as a focus for precipitation of lime salts 
from the saliva. 

The correct physiological method, however, of pre- 
venting such deposition would be to increase the carbon 
dioxide content of the saliva, since it is owing to a 
deficiency of this gas or its rapid escape from the saliva 
that the precipitation of the lime salts occurs. Exactly 
in what ways this may be done is not at present clear ; 
but this much is quite probable — that the amount of 
carbon dioxide in the saliva is dependent upon muscular 
metabolism ; and that the carbon dioxide is derived from 
the blood-stream and is not manufactured in the glands, 
since during stimulation the blood flowing from the 
glands assumes a bright red arterial colour. Therefore 
muscular activity of the body generally should lead to 
a decreased tendency to deposits of calculus. Clinical 
experience lends at least a negative support to this, for 
such deposits are usually seen in two classes of people : 

1. Those in whom there is a localized oral stagnation 
owing to loss of function. 

2. Those in whom salivary secretion has been normal 
and has protected the teeth during early life, but when 
the more sedentary period of life has arrived (causing, 
presumably, a decrease of carbon dioxide formation 
and excretion) the lime salts have been precipitated. 
That is to say, the alkalinity and phosphatic indices 
may remain normal, but their solvent carbon dioxide has 
diminished to its minimum point. 



The mouth might be inoculated* with the defin'te pur- 
pose of either (i) introducing organisms which should 
exert an antibiotic effect upon the established organisms ; 

(2) introducing organisms which would decompose 
carbohydrates, with the formation of alkaline products ; 

(3) introducing organisms which would rapidly remove 
the carbohydrate debris before lactic acid could be 

1. As regards the first possibilit} 7 , although the forces of 
antibiosis are known to exist — in fact, must exist — in the 
mouth to a very large extent, it seems (at present) to be 
the rule that " pathogenic " organisms are the ones 
which are crowded out or succumb, and that the organ- 
isms of caries are the ones which survive. We do not 
yet know enough about the biological characters of 
mouth organisms alone or n combination, in the mouths 
of immune individuals and of susceptible individuals, to 
be able to say which, if any, are inimical to the acid- 
forming group responsible for the primary decalcification 
of enamel ; or whether any organisms exist which, if 
introduced into the mouth, could be induced to establish 
themselves and exert such an action. This is a subject 
which will probably be shown to have possibilities when 
it is thoroughly worked out. 

* The word " inoculate " is used here, not to mean hypo- 
dermic inoculation, but simply the insertion of organisms in the 
oral cavity preferably by their being rubbed between the teeth. 



2. As regards the second possibility — the introduction 
of organisms which might from carbohydrates produce 
alkaline end-products — there are two classes of bacteria 
which might conceivably bring this about. 

Firstly, some of the hyphomycetes (moulds). It has 
been observed on many occasions, that in the experi- 
mental production of caries, when moulds establish 
themselves in the bread and broth mixture, the reaction 
becomes alkaline. Attempts have therefore been made 
to isolate the organisms responsible for such a change 
■ — so far. however, quite unsuccessfully. 

The second class is the mesenteric group of organisms. 
These, as has been well known at least since Goadby * 
some years ago carefully worked out their biology and 
cultural characteristics, in a carbohydrate medium pro- 
duce an alkaline reaction. 

It seemed, therefore, at first that in this group were 
organisms well adapted to the purpose of neutralizing 
the effects of the lactic-acid-forming organisms, and some 
work was undertaken along such lines. It has, however, 
for the present, at least, been abandoned for the following 
reasons : 

(1) Although an alkaline reaction can be obtained 
when the organism is in pure culture, when it is mixed 
with anything approaching a " normal " amount of 
acid-forming organisms the reaction is always acid ; that 
is to say, the acid-forming group seem to be the more 
vigorous, and able largely, if not entirely, to suppress 
the carbohydrate decomposition by the mesenteric 

This, indeed, is what one would expect, seeing that 
the mesenteric group of organisms are widely distributed, 
both in milk and water, and are practically always 
present in the mouth, presumably partly by inoculation 
and partly by becoming established. It would therefore 
appear to be obvious that under ordinary conditions the 
mesenteric group cannot obtain the upper hand, since 
* "Mycology of the Mouth," London, 1903. 


the reaction produced by mixed mouth organisms, from 
immunes as well as susceptibles, with carbohydrates is 
always acid. Until, therefore, we can by some means 
definitely reduce the vitality of the acid-forming organ- 
isms without affecting the mesenteric bacilli, inoculation 
with such organisms would seem to be useless. 

(2) The organisms are powerfully proteolytic ; in fact, 
they are the ones which are largely responsible for the 
digestion of the collagenous matrix of the dentine. In 
view of this fact and of the important role which has 
been assigned to Nasmyth's membrane, it does not 
seem wise to employ organisms which would destroy 
the latter structure. (Especially would this be likely 
to occur in positions where the membrane is not removed 
by attrition, and where, therefore, its presence is required 

3. The Introduction of Organisms which rapidly break 
up the Carbohydrate Debris, with the Formation of In- 
nocuous Substances. — Many of the higher organisms — 
hyphomycetes and blastomycetes — have the property of 
transforming certain carbohydrates into carbon dioxide 
and alcohol. 

The commonest and most familiar example of this is 
the fermentation of sugars by yeast. The equation 
which expresses in general terms the action which takes 
place is — 

C 6 H 12 6 =2C 2 H 5 .OH + 2 C0 2 . 

This does not express exactly what occurs under all 
circumstances ; a certain proportion of the sugar, for 
instance, is consumed and assimilated by the organisms, 
and another portion is converted into by-products. 
These are, however, in all cases trifling in amount, and 
consist of glycerine and traces of succinic and acetic 
acids, the latter not amounting to more than 07 and 
0-05 per cent, respectively of the total quantity of sugar 
transformed into alcohol and carbon dioxide.* More 

* Oppenheimer : " Ferments and their Actions," p. 248 et seq. 


by - products are, however, produced by the mucor 
species than by the saccharomyces group. 

There seems to be no reason why some variety of the 
saccharomyces group should not be utilized for the 
purpose of breaking up the carbohydrate debris in the 
mouth into carbon dioxide and alcohol. Various forms 
of saccharomycetes are occasionally found in the mouth, 
but there is no evidence to prove that they exert any 
harmful action, except in the case of Saccharomyces 
albicans, the organisms of thrush, and then only in weak, 
debilitated individuals. 

Goadby* has noted the presence of a yeast in a very 
few cases of pyorrhoea alveolaris. but of what particular 
variety is not mentioned, except that in two cases it 
was pathogenic for guinea-pigs. But, as the same' 
observer has also shown, the infections in such cases 
are always very mixed ones, and it is not suggested 
that all the organisms found are causative factors ; 
moreover it is recognized that pyorrhoea alveolaris 
is usually found in mouths relatively free from 

Millerf has noted the presence of saccharomycetes in 
the mouth, and stated that he regarded them as " the 
most harmless of all mouth parasites." 

It is now known that yeasts may be beneficially 
given internally (the dose being 5 to 10 grammes 
in milk) in order to increase the opsonic power of the 
blood, and to promote a leucocytosis ; and boils have 
been successfully treated in this manner. If, then, it 
can be shown that opsonins pass into the saliva, the 
administration of yeast may be of indirect advantage in 
raising the " opsonic index of the saliva." 

Saccharomycetes as a class require for their nourish- 
ment (besides carbohydrate) water; a source of nitrogen, 
preferably in the form of albumin ; and various inorganic 

* "Mycology of the Mouth," p. 178 ; Erasmus Wilson Lec- 
ture, British Dental Journal, 1907, p. 895. 

| " The Micro-Organisms of the Human Mouth," p. 345. 


substances, such as iron, potassium, magnesium, phos- 
phorus, and possibly sulphur.* 

The saliva as a medium practically fulfils these 
requirements. It has, too, been shown by Harden and 
Young f that the alcoholic fermentation of glucose is 
carried on more rapidly in the presence of phosphates, 
of which saliva contains an appreciable quantity. 

Moreover, for promoting the solution of starch debris in 
the mouth there would seem to be a particular fitness in 
combining a saccharomyces with the saliva. Morris t 
has shown that ungelatinized starch granules submitted 
to the simultaneous action of diastase and yeast may 
have three times as much dissolved from them as by 
diastase alone. 

The variety of organisms which I think is most suited to 
the purpose under consideration is Saccharomyces coagu- 
latus. This organism occurs " wild," mixed with moulds 
and tOrulae growing on wet wood surfaces ; it is found 
also mixed with other yeasts, such as are used by brewers 
and bakers. 

I have obtained it in pure culture by the following 
means : A sample of mixed yeast is obtained and 
examined to see if it contains bacteria as well as sac- 
charomycetes. The former may be got rid of by the 
usual method of plating out at room temperature on 
glucose agar or gelatine to which 10 per cent, glucose 
has been added. The yeast may also be purified by 
taking successive subcultures in 10 per cent, glucose to 
which a trace of bouillon has been added and which is 
kept at room temperature. This favours the development 
of the yeast, but not of the bacteria. The yeast having 
been obtained in a practically pure state, it is heated to 
50 C. for one hour, at which temperature all other 
varieties but S. coagulatus are destroyed. Subcultures 
are now taken, and a pure culture should result. 

* A. Mayer, quoted by Oppenheimer, loc. cit., p. 209. 

t British Medical Journal, 1909, p. 1376. 

\ G. H. Morris, Journal of the Chemical Society, vol. lxxix., p. 1085. 


S. coagulatus is spherical to oblong in shape, and is 
somewhat smaller than ordinary yeasts, being about 
5 to 6 /x in diameter (Fig. 57). It does not grow very 
rapidly, and in fluid media does not cause turbidity ; the 
whole of the growth is either attached to the side of the 
glass tube or is in a compact mass at the bottom. 
Gentle shaking of the tube causes no turbidity. 
Vigorous shaking is necessary in order to dislodge the 

Fig. 57. — Saccharomyces Coagulatus. 

colonies ; even then they are in obvious particles, and, 
like a heavy precipitate, soon settle to the bottom, 
the liquid becoming clear again. This behaviour is 
quite sufficient to distinguish a pure culture of it from 
nearly all other organisms. 

It is difficult to obtain any of the growth on the 
platinum needle, and it is somewhat resistant of emulsifi- 
cation on the slide, in this respect reminding one # of 
Staphylococcus viscosus. It acts well as a ferment at 


body temperature, and can carry the fermentation of 
a solution to a very advanced point — farther in some 
cases than S. cerevisice is able to do.* 

Cultures of the organisms may be spread out on a 
filter-paper and dried (avoiding contamination). Their 
vitality is thereby somewhat lowered, but is soon 
regained when placed in a culture medium. 

The dried cultures may be pulverized, and the mouth 
inoculated with the powder ; at present I have used only 
about 10 grains, but I think probably this dose may 
be considerably increased with advantage. It has a 
distinctive but not unpleasant flavour. 

The following experiments, amongst others, have been 
made with Saccharomyces coagulatus in order to deter- 
mine its possible beneficial action in the mouth. 

I. The Rapidity of Consumption of Carbohydrates. 

(a) Two tubes, A and B, containing 10 per cent, 
glucose medium, were inoculated with saliva and 
saccharomyces respectively. The tubes were connected 
with graduated test-tubes inverted in water, and were 
then hermetically sealed. The whole was then placed in 
the incubator for three days, by which time — 

Tube A (saliva culture) had formed 1*6 c.c. of gas. 
Tube B (yeast culture) had formed io-2 c.c. of gas. 

That is to say, that a considerable amount of carbo- 
hydrate had been used up in B to form carbon dioxide 
which might otherwise have been utilized for the for- 
mation of lactic acid. 

(b) Two tubes, A and B, each containing 0-5 gramme 
of glucose equally diluted, were inoculated respec- 
tively with one loopful of " materia alba " and one 
loopful of the yeast, and were connected to the 

* Matthews : " Alcoholic Fermentation," p. 30. 


gas-collecting apparatus. The following gas forma- 
tion and sugar consumption occurred in forty-eight 
hours : 


Gas Formation. 

Sugar Consumption. 

0*047 gramme. 

A (mouth organisms) 

B (yeast) 

2 C.C. 

21 ,, 

In B tube, therefore, in forty-eight hours 78 per cent, 
of the total sugar had been fermented, whilst in A tube 
only 9 per cent, had been used up ; and in B tube ten 
times as much was converted into gas as in A. These 
volumes of gas are only relative, and not absolute, since 
a good deal was absorbed by the medium and the water 
over which it was collected. 

This absorption of C0 2 by the medium causes it to 
have an acid reaction to litmus, but that this is negligible 
as a decalcifying agent was proved by the fact that teeth 
kept in such a medium for one week showed no sign of 
decalcification of the enamel. 

Nevertheless, in impure cultures of yeast with other 
organisms various acids are formed, especially in vitro, 
by the decomposition of the retained alcohol ; acetic acid 
is the one chiefly formed, according to the equation 

CH 3 .CH 2 .OH +0 2 = CH 3 .COOH + H 2 0, 

acetaldehyde being an intermediate product. 

This, however, is extremely unlikely to occur in the 
mouth, especially if there be a good salivary circulation, 
since the alcohol, being an extremely light, diffusible, 
and volatile liquid, would rapidly disperse, and be carried 
away in the saliva or evaporated. 

The following experiments, too, show that it would be 
extremely unlikely to be retained. 



2. The Dispersion of the Carbohydrate Debris by the 
C0 2 Formation. 

In order to measure the rapidity of the action, short 
pieces of quill tubing, 0-5 centimetre in length, were 
filled with mixtures of carbohydrate and organisms 
coloured with litmus, and suspended horizontally by 
means of threads in 0-45 per cent, sodium chloride 
solution (to represent saliva). They were then placed in 
the incubator, and the time taken for the short tubes to 
become empty was observed. 

(a) Biscuit was insalivated, and tube A filled with the 
mixture. To the remainder of the mixture (about 
0-5 c.c.) one loopful of 5. coagulatus was added and 
thoroughly mixed. Tube B was then filled with the 
fresh mixture, and both were hung in the salt solution 
and incubated. 

A tube remained full, although strongly acid, for ten 
days. B tube was emptied in twenty-six minutes (this 
being the average of six observations). 

B tube was filled again with a similar mixture, but 
containing half the amount of yeast. It was empty in 
three hours. 

(b) Saliva was inoculated with 5. coagulatus, and sub- 
cultures taken also in saliva ; after twenty-four hours 
biscuit was triturated with the subculture, and tubes 
filled with the mixture as before and incubated. They 
both became empty in twelve hours. 

(c) Similar experiments were conducted with teeth 
fixed together with wax in normal position so as to form 
interdental spaces (as nearly as possible equal in size). 
The spaces were then filled with similar mixtures to the 
above, and the times taken for the spaces to " clear " 
observed as follows : 

Space A (biscuit and saliva), clear in eight days. 
Space B (biscuit and saliva, one loop yeast), clear in 
forty-five minutes. 


Space C (biscuit and saliva subculture of S. coagulatus), 
clear in twenty-one hours. 

Space D (biscuit and saliva, trace of S. coagulatus), 
clear in forty-eight hours. 

It is evident, then, from these experiments that the 
presence of the organism S. coagulatus in the saliva 
very materially increases the rapidity with which 
carbohydrate material may be broken up and removed 
from between the teeth. Once being removed, and 
there being an efficient salivary secretion, it will be 
swallowed and digested. 

Undoubtedly, at first a large number of the organisms 
would also be removed similarly and swallowed; but this, 
I think, would tend to become less as the organisms 
became established in the mouth, since, as has already 
been described, this organism tends to form " plaques," 
or, as its name implies, to coagulate and to adhere to 
the glass of the tubes, and it would probably do the 
same on the teeth in the mouth. 

This investigation is not yet complete, but I think 
sufficient evidence has been bi ought forward to show 
that there is every probability of the method being an 
extremely valuable asset in the preventive treatment of 
dental caries. 

There is. I think, some ground for inferring that some 
of the native races owe their immunity to the presence 
of such organisms in the mouth. For instance, it is a 
custom found amongst certain races for the women with 
the cleanest mouths to insalivate the material from 
which it is desired to produce alcohol, in order to start 
it fermenting. Although the ordinary mouth organisms 
with sugar do form a trace of alcohol, yet it is merely a 
trace, and would not be sufficient, I think, under any 
circumstances to form an intoxicating beverage ; and in 
any case the lactic acid produced would be so much in 
excess as to render the fluid far more sour than alcoholic. 







Although no race may be said to be absolutely im- 
mune to dental caries, yet in some races — namely, the 
Esquimaux and the Maori — it is so extremely rare, 
compared with the enormously high incidence amongst 
European races, that a practical immunity may with 
reason be claimed. 

It has been customary for some years now — since the 
researches of J. R. Mummery — to believe that those 
races which consumed most meat were the most immune, 
and vice versa; but, as we shall see, this is on strict 
inquiry by no means the case. 

The Maori Race. 

Instead of discussing vaguely the dietaries of all the 
various races more or less immune to caries, it will be 
much more profitable to confine our attention firstly to 
a detailed investigation of a single race having a high 
immunity. We shall, too, learn much more of value 
from a study of the dietetics of a people whose diet was 
a mixed one, with carbohydrates preponderating, and 
for whom climatic conditions were similar to those for 
Europeans. Such a race is the Maori, in whom, as we 
have seen, the average incidence of caries may be placed 
at i*2 per cent. In Mummery's investigations the diet 
is inferred to be largely a protein one, since the Maoris 
were cannibals ; and this seems to be the reason ascribed 
by Mummery for their comparative freedom from caries. 



Such an assumption, however, is not founded upon 
facts ; the Maori was essentially a mixed feeder, and 
carbohydrates largely preponderated. 

The consumption of human flesh only occurred on 
more or less rare occasions after a war-party had returned 
home with prisoners, and then not all the prisoners were 
eaten ; a large number were always reserved as slaves. 
But most important of all, from our present point of 
view, the consumption of such food was confined almost 
entirely to the warriors. Human flesh was strictly tafiu 
— i.e., forbidden — to women,* and only the elder boys 
were allowed a very small portion. Yet, as a matter of 
fact, both women and children had just as good teeth as 
the men. This disposes completely of any theory that 
the Maoris owed their immunity to caries to cannibalism. 

The perfection and also the marked attrition of the 
teeth of this race have been also ascribed by some 
observers to the mastication of coarse fibrous food, such 
as fern-roots, mixed with sand. True, they ate fern- 
root, and also their " ovens " are frequently found among 
sand-dunes, but neither of these things justifies the above 

The staple food of the Maori was undoubtedly the 
kumara, or sweet potato (Ipomcea chrysorrhiza) ; this 
was cultivated with great care. It was sun-dried and 
either eaten at once or stored for winter use. 

The rarauhe, fern-root (Pteris aquilina or esculenta), 
was the next important source of food, but it is very 
necessary to note the method of preparation. Young 
roots only were selected, and of these only those having 
the least fibre. If the root did not break crisply, it was 
forthwith discarded. The roots were dried and roasted, 
the outer skin scraped off with a shell ; it was then 
pounded to a powder, and all fibres carefully removed. 
Water was mixed with it in order to make a kind of 
dough, and it was then cooked. Before being eaten it 

* Onlv one woman — the high-priestess — was ever allowed 
this " privilege." 


was as a rule flavoured with the juice of the tutu berry, 
or with the juice of the ti-tree root, the former having 
an acid taste, and the latter a su'eetish acid taste. 

Taro was another vegetable cultivated by the Maori 
and largely consumed ; it was a perennial, was therefore 
always eaten fresh, and had a strong and distinctive 

The roots of seedling ti-trees were also eaten after 
being baked ; these contain a sapid sugary juice much 
valued as a flavouring agent. 

Two kinds of bread were made — one from the pollen 
of the bulrush, and the other from the berries of the 
hinau-tree ; the latter had a very pleasant taste, and 
the former was said to taste like gingerbread and sweet. 

Hue, a pumpkin-like fruit, was in the summer season 
consumed in enormous quantities. A large number of 
different kinds of berries were also eaten raw ; these all 
had acid sapid properties. The berries of the following 
trees were the most favourite varieties : the kutukutu 
[Fuchsia excorticata), the karaka (Corynocarpus laevigata), 
the poroporo and the poporo (Solarium aviculore and 

A jelly was also made from a form of edible seaweed 
called karengo ; the latter was first stewed, and then 
soaked in tutu juice before being eaten. 

But it is not to be supposed that the Maori was a 
vegetarian : far from it. Yet since there were practically 
no mammals indigenous to New Zealand,* his animal food 
consisted entirely of fish and birds, to obtain which he 
went to considerable trouble. The difficulty, however, 
in obtaining such food must have been so great in many 
cases as to preclude the possibility of its forming any- 
thing but a subsidiary part of his dietary. For instance, 
the Maori used no projectiles of any sort, and all his 
birds were either snared with a loop on a long pole or 

* A very small rat and a dog were indigenous at least as far 
back as legend and history go ; both these animals were eaten, but 
the latter was tapn as an ordinary article of diet. 


speared with a long light spear. In this way were obtained 
the following : kukupa (pigeon), kaka (parrot), putangi- 
tangi (paradise duck), pukeko (swamp-hen), kiwi 
(apteryx . weka (wood-hen), koreke (quail . Also a large 
number of young sea-birds, including "mutton " birds, 
were collected in season, and dried for winter use. The 
birds, however, it will be noticed, were all rather small, 
and. with the exception of the putangi. several would 
be required to make a meal for a family. 

As regards fish, the Maori used small nets only in 
rivers and estuaries, and a line and hook in salt water. 
The hook was not " baited " as we understand it, but 
simply had a piece of iridescent paua-shell attached ; 
and thus were caught hapuka (cod), barracouta. moki. 
patiki (flat nsh\ and also snapper, kingnsh. and butter- 
rlsh. Sharks were occasionally caught, and were 
esteemed a great delicacy. The inland tribes depended 
upon fresh-water fish, of which eels were the chief varietv. 
These were trapped as a rule in weirs constructed of 
reeds. Piharau (lamprevs) were also caught similarlv. 
By means of small seine nets were also caught inang 
kind of whitebait) and upokororo (a kind of grayling). 

Crayfish and shellfish also formed a part of their 
regular dietary, especially the paua. a large clam ; 
these were collected, sun-dried, and stored, and also 
sent inland to other tribes in return for " potted " birds. 

Cooking. — Most of the animal food was cooked 
together with " vegetables.'' such as kumara. taro, 
raruake. by being steamed in an earth oven for about an 
hour and a half. Some of the larger birds were roasted 
on a spit. One of the chief aims in the process of cooking 
was to keep all the " flavour " in by wrapping the food 
in layers of green leaves, and covering the oven with 
mats and earth. The leaves having once been opened, 
the food was either eaten or thrown away ; no food was 
ever recooked or touched a second time upon any 
consideration whatever. 

The Maori was allowed to exercise his idiosyncrasies of 


taste, and was not bound by any custom or law to eat 
what he did not relish ; he simply stated that he was 
" wainamu " for certain food — even human flesh in 
many instances — and that wish or declaration was 
accepted by parent, host, or guest, without demur. 

As a rule two meals a day were taken, at ten and four 
o'clock ; in times of scarcity this number was reduced 
by half. As regards drinking, the Maori drank only 
plain water, or water flavoured with the juice of the 
tutu berry. 

Masticatories were largely indulged in. The gums of 
the kauri and tarata trees were freely chewed, as also 
was bitumen, these being passed unceremoniously from 
one mouth to another. I have been unable to gather 
any evidence either from the Maoris themselves or from 
other observers that they ever practised cleaning the 
teeth by any artificial means. 


Thus it is obvious — 

1. That the dietary was essentially a very varied 

2. That the Maori could not possibly have owed his 
immunity to a preponderance of animal food. 

3. That the methods of preparation of vegetable and 
carbohydrate food generally was such as to eliminate all 
the obviously coarse and fibrous constituents ; neverthe- 
less, since the methods of preparation were of necessity 
crude, a certain amount of the finer particles of cellulose 
must have remained in all their food, even in the bread. 
That nearly all food was steamed, thus considerably 
reducing its toughness. 

4. That a considerable amount of fruit and berries 
was consumed. 

5. That throughout the whole dietary one of the most 
important factors was taste and flavour. (The character 
of the food, both protein and carbohydrate, was such as 


had in itself distinctive flavours — namely, fish and game, 
sweet-potato and fern-root, berries and fruit.) That, in 
addition to this, substances, such as the tutu and ti-tree 
juices, were constantly used to increase the sapidity of 
the ordinary food. 

6. The use of the tutu berry juice is particularly 
interesting ; there is no doubt that it acted as a stimulant 
of alkaline saliva by reason of its acid-sweet flavour. 
But it also in all probability had a further influence on 
the salivary secretion through the action of its active 
principle, tutin, on the nervous system. Fitchett* 
found that after hypodermic injection of tutin in the cat, 
among the first symptoms in five cases out of six was 
intense salivation. And from the character of the saliva 
it was thought that it probably arose from sympathetic 

Now, although there should be very little tutin in the 
juice of the berry, I think that undoubtedly some is 
very frequently adventitiously present, judging from 
the cases in which toxic symptoms have arisen in 
Europeans after sucking the berries or drinking wine 
made from the berries when great care had been taken 
to exclude the seeds. Fitchett also showed that tutin 
was not excreted at all rapidly. It would therefore 
appear to be not at all improbable that the Maori, by 
the constant ingestion of even minute quantities of 
tutin, kept the efferent salivary nerves in a state of 
excitability, if not of mild excitation. 

7. The use of masticatories also undoubtedly kept the 
salivary glands in a state of activity, and both their 
secretory powers and the total daily amount of secretion 
would be thereby greatly increased. 

Moreover, the habit of chewing prevented " stag- 
nation " within the oral cavity, and so removed one of 
the great predisposing factors to disease. 

* " Physiological Action of Tutin," by F. Fitchett, M.D., 
Transactions of the New Zealand Institute, 1908. 



It is therefore clear that the relative immunity of the 
Maori was due, not to an excessive protein diet nor 
to a great excess of hard, fibrous, inert matter in their 
carbohydrates, but to the habitual and constant masti- 
cation of salivary stimulants, thus producing a constant 
flow of alkaline and diastatic saliva, the beneficial effect 
of which has been previously considered. 

Other Races. 

It will be found upon close investigation that similar 
dietetic principles to the above pervade almost every 
" natural " race; and although it is not possible here to 
consider in similar detail the foods of all other races 
having a comparative immunity to caries, yet a brief 
consideration of the various dietaries is important. 

Esquimaux.— It is quite usual to suppose that the 
Esquimaux exist entirely upon animal flesh, fat, fish, 
and birds. A little thought, however, will show that 
this cannot be so ; no one can be entirely deprived of all 
fresh carbohydrate food without ill results, and, indeed, 
investigation shows that the Esquimaux themselves 
recognize this. Kjellmann says that no less than twenty 
different kinds of plants are used for food, and that 
" provisions of berries and of reindeer moss rich in starch 
are stored up for the winter." The berries are a kind of 
small cranberry, the acid-sweet taste of which is well 
known. They also brew a fermented liquor something 
like sauerkraut. (Incidence of caries, 1-4 per cent.) 

With the Lapps it is customary to supplement their milk 
with sorrel or bittterwort, and Ratzel affirms that " similar 
acid or pungent plants are welcome to all polar people." 

The inland Arctic people of North Asia live largely on 
bilberries, supplemented by the products of hunting and 

The Samoyedes, a nomad Arctic people, unlike the 


Esquimaux, have numerous wives, whose duty it is, 
whilst the men fish, to seek for shells, herbs, and berries. 

The Indians of the North-West American Coast are 
very Esquimaux-like in their diet, subsisting largely on 
fish, supplemented by roots, grasses, and berries, and a 
cultivated potato-patch is usually attached to each 
" house." All food is cooked by the steaming process. 
As a masticatory the wood of the sugar-pine is chewed, 
which travellers assert tastes as much of turpentine* as 
of sugar. (Incidence of caries, 3-9 per cent.) 

The Fuegians, inhabiting the other extremity of the 
American coast, are also said by some travellers to exist 
chiefly on fish partially cooked, to which is ascribed 
their broad zygomatic arches and powerful masticatory 
muscles. Darwin, however, whose accuracy as an 
observer cannot be doubted, says that (at least when he 
visited Tierra del Fuego in 1834) their staple food was a 
dried and hardened fungus (Cyttaria Darwinii), which 
has " a mucilaginous, slightly sweet taste, with a faint 
smell like that of a mushroom." 

Oceanians, Polynesians, and Melanesians.— Here 
again it is popularly imagined, because many of the in- 
habitants of the Pacific Islands were (and some still 
are) cannibals, that their diet was essentially a protein 
one. On the contrary, as with the Maori, human flesh 
was consumed only on very special occasions, such as 
after a raid on a neighbouring island or at the opening 
of a " tambu " house or other high festival. Those who 
have lived in the islands are all unanimous that by far 
the larger proportion of food in all cases consists of 
vegetables and fruit. 

The Fijians, perhaps, are the largest meat-eaters of 
all of the islanders. The greatest proportion of their 
animal food consists of fish, then opossums, and less 
frequently pigs. All meat is cooked, usually steamed 

* The important pharmacological characteristic of turpentine 
in this respect being that in the mouth it has a pungent, bitter 
taste, and causes a reflex flow of saliva. 


until very tender ; the opossum is said to have a 
"strong flavour," and their roasted pig is thought by 
some to be superior in flavour to English bacon.* 
Meat is frequently eaten in a half-putrefying condition. 
But even the Fijians' food is principally vegetable, of 
which the following are the varieties chiefly consumed : 
taro, yams, sweet root of ti-tree. banana, sugar-cane, 
and cocoanuts. 

Most of these vegetables and fruits are common to all 
the islanders, some kinds being more cultivated in particu- 
lar islands than others. Poi. a kind of sour porridge, is 
made by most Polynesians from taro flour, by allowing it 
to ferment. Sago is largely eaten by some tribes ; it is 
most carefully prepared and cooked, the coarse fibres 
being removed first of all by an ingenious system of 

In some parts of Polynesia (particularly in Tahiti) 
breadfruit is fermented into a sour paste and set aside 
to store, since in this condition it keeps well. 

Fruits, of course, form a large and important part of 
these islanders' dietary. In addition to those already 
mentioned are the mango (a large pumpkin), a variety 
of cucumber, a species of lime, the kernels of the 
borolong and saori. the fruit and leaves of the asi-tree, 
these having a decidedly acid taste, and many others. 

Nearly all Polynesians season their dishes with salt sea- 
water. (Incidence of caries, 5-2 to 19 per cent.) 

Kava. an alcoholic beverage of bitter or sour flavour, is 
largely consumed in a great number of the islands. It is 
prepared from the roots of the Piper metliysticum ; in 
order to induce fermentation the roots are chewed by 
women and girls, then expectorated into a bowl or 
trough, and water is added (this method, however, is not 

The Chinwans of Formosa also brew a fermented drink 
from rice and millet, yeast being replaced by the saliva 
of an old woman in a similar manner to the above. A 
* Guppy, " Solomon Islanders," 1883. 


like custom is observed among the Indians of Central 
America in Guiana, where an intoxicating beverage 
called " paiwari " is made in a similar manner from 
cassava bread, the fruit of palms, maize, and bananas. 
In this case the mass is sterilized, by pouring on boiling 
water, before being chewed by the women. It is said 
to be a " cooling " drink somewhat resembling sour beer. 

The Papuans have as their staple food the kumara 
and sago, diversified by large broad-beans and the leaves 
of the tree-cabbage. A kind of palm is cut down when 
they are hungry, and the inside leaves of the top green 
shoot are eaten ; these are " straw-coloured and like 
asparagus, sweet and slightly dashed with acid ;" of 
this the natives eat great quantities. Bread fruit is 
eaten boiled ; this is said to be palatable, though slightly 
bitter. The Papuan, however, is extremely partial to 
animal food, but it is necessary to observe the conditions 
under which it is eaten. 

The pig, cassowary, and wallaby are hunted by being 
driven into corrals made of nets set in the forest. The 
game is roasted, and in an incredibly short space of 
time every particle is eaten, and the people then lie 
about in a gorged condition. Such " drives " only 
occur at long intervals. Papuans are also very fond of 
a large tropical beetle (one of the Passalidae) found in 
decaying tree-trunks ; it is usually eaten raw, but may 
be just warmed in the fire ; the flavour resembles that 
of a lemon. 

Malays.— The staple food of the wilder tribes of the 
Malay Peninsula consists chiefly of such wild yams, 
roots, and fruits of the jungle as may be in season. 
When this fails, the men engage in hunting, trapping, 
and fishing. In other more agricultural tribes, rice, 
maize, millet, tapioca, and bananas form the staple 
articles of diet. 

The Semang tribes exist on small birds and animals, 
various kinds of yams and roots, with the addition of 
gourds, pumpkins, chillies, maize, and sweet potatoes. 


The Sakai live upon wild tubers, roots, and fruits, 
and some animal food ; they do not, as a rule, search for 
game until everything else fails. One kind of apple-like 
fruit eaten is said to be very pleasant, but to leave a 
most decided " after-taste." 

Jakun peoples, like the two former tribes, are markedly 
frugivorous. Logan gives lists of forty and sixty-nine 
different kinds of fruits which various Jakun tribes are 
in the habit of eating. The latter tribes eat more rice 
and less meat than the two former, but the rice is 
always flavoured. Skeat says : "I have myself fre- 
quently seen the latter at their meals, when their only 
food consisted of boiled rice seasoned with acid fruits 
obtained from the jungle." Other seasonings used are 
kulim-leaves (resembling onions), wild ginger, turmeric, 
species of eugenia, wild pepper, and various spices. 
When the people disperse, as they do each year, for long 
periods through the jungle in search of fruits, they live 
entirely upon tapioca root and fruit. Favre, however, 
speaking of these tribes, says that their diet is very 
varied, and nothing can be said to be regular, and when 
opportunity arises they will eat the flesh of any available 
animal. Honeycomb is greatly prized, but it is not 
eaten until the small bees are well formed in the cells ! 

The tribes on the seaboard exist on rice principally, 
to which is added the flesh of the hog, monkey, snake, 
and birds, together with vegetables and wild fruits. All 
these tribes have a great desire for the durian fruit, some 
living upon it entirely for six and eight weeks, and in 
one case Thomson found six boat-loads of Sea- Jakun, 
who had travelled 180 miles by sea to obtain this par- 
ticular fruit. 

The Indians of North and Central America. — It 
is stated by Mummery that the diet of the North 
American is mainly meat ; with this Ratzel does not 
agree. Although this authority admits that animal 
food is eaten with avidity, yet he states that the chief 
article of diet is still the maize, and that large quantities 


of fruits, berries, and nuts, are collected, and also stored 
for winter use. Wild melons, plums, and grapes, are 
recognized food items for tribes in the interior. 

Greatly esteemed is the large bulb of the Lilium 
columbianum and the bulbs of other lilies ; in addition, 
the roots of the sunflower, white clover and bracken, 
wild onions, and wild carrots, are largely eaten. 

A great variety of berries are gathered and eaten, 
both fresh and preserved, the most favoured being the 
" Service " berry — a kind of black currant {Amelanchier 
alnifolia) ; in addition, the following are also eaten : 
red and black currants, gooseberries, blackberries, straw- 
berries, raspberries, whortleberries, soapberries, cran- 
berries, crowberries, chokeberries, elderberries, bear- 
berries, jumperberries, roseberries, mooseberries. and 
salalberries. (The latter is a species of Gaultheria.) 

The food of all Neu Mexicans (Indians) is similar. 
They make pretensions to agriculture, and are used to 
a vegetable diet ; they seldom, however, raise sufficient 
to last until the new crops are available, and so have 
to subsist on " beans, nuts, and other wild fruits, which 
they collect in considerable quantities." Of animal 
food, comparatively small quantities of rats, lizards, 
squirrels, and fish are eaten. 

In Central America also the Indians much prefer 
meat, but " totemism " frequently prohibits many 
animals. In addition, the quinoa and the potato are the 
chief natural food of these races ; manioc and cassava 
are also used ; and in Chili it is said that the strawberry. 
which covers miles of country with its runners, is an 
important article of food. The fruit of the carnahuba 
and mariba palms are, too, favourite articles of diet ; 
these have an agreeable juicy, sweet flesh, and are utilized 
in various ways. 

Wild tribes of Central America, according to Ban- 
croft, are essentially agricultural, living on maize, beans, 
bananas, and plantains, together with a variety of fruits 
and roots. Fish, eggs, turtles, and fowls, with the 


inevitable chilli (and salt) for flavouring, compose their 
animal dietary. 

The " Natural " Races of Africa. — The diet of the 
negro in general may be said to be both animal and 
vegetable, with wide variations for the various races, 
some races consuming a minimum of carbohydrates, and 
others a minimum of flesh protein. Nearly all races. 
except the Bushmen, Dwarfs, Masai, and Galles, cultivate 
the following crops extensively : millet, maize, manioc, 
and banana (Equatorial). Coffee, guru, and kola nuts are 
habitually chewed by many races ; salt (sodium chloride) 
is in great demand as a seasoning by all, and when this 
cannot be obtained potassium salts obtained by evapora- 
tion of lake water are substituted. The practices of 
smoking Cannabis indica and of brewing beer by the 
fermentation of maize or millet are found in very many 

Some races clean the teeth and scrape the tongue 
artificially with a frayed-out stick dipped in ashes, and 
spend a considerable time each day on the process. 

The natives of British Central Africa eat " surprising 
quantities " of a stodgy kind of porridge made from 
maize or millet flour, but do not at all like it without 
salt or some form of ndiwo (relish). Sweet potatoes 
and manioc root (raw and cooked) are also eaten, and 
in the spring pumpkins, gourds, and cucumbers are prin- 
cipal articles of diet ; but comparatively small quantities 
of meat are eaten, and then it consists chiefly of rats, 
very high fish, locusts, white ants, and occasionally 
fowl or goat's flesh. 

In Uganda the natives in many parts (Waganda) have 
advanced somewhat higher in the scale of civilization 
and its arts ; they are " mixed feeders." living on the flesh 
of domesticated animals, such as sheep, goats, and fowls, 
together with bananas, maize, sweet potatoes, yams, 
and various fruits. 

The Manganga (around Lake Nyassa) eat vegetables 
chiefly ; they consume neither eggs, milk, nor poultry. 


They catch and dry great quantities of fish, which, 
together with salt, they trade to other tribes in the 
interior at great distances. 

The Kaffirs and Hereros are essentially cattle-breeders, 
but are extremely reluctant to slaughter animals merely 
for their own food ; at feasts, however, and on special 
occasions they will consume enormous quantities of 

The usual morning and evening meals of the ordinary 
Kaffir consist of a porridge and amasa (sour milk), one 
or other vegetable, millet " beer," and occasionally some 
meat. (Incidence of caries, 14-2 per cent.) 

The Negroes of West Africa also live on grain, chiefly 
supplemented by aromatic herbs and much salt. Cayenne 
pepper is very popular. 

The Bushmen are a fierce nomad people living chiefly 
on the product of the chase, supplemented by edible 
roots, honey- — a very favourite and frequent article of 
diet — and a wild water-melon, juicy and bitter in flavour. 
They cover great distances in their marches, and suffer 
considerable privations, and the water-melon is said to 
be frequently their only possible drink. (Incidence of 
caries, 20-6 per cent.) 

The Pygmies of Central Africa are likewise a nomadic 
tribe, living chiefly on the products of the chase, some 
of which they exchange with adjoining agricultural tribes 
for plantains, potatoes, etc. ; their own carbohydrate 
supply consists of fruit, nuts, and honey. 

The Abyssinians are mixed feeders, and are more 
highly civilized than other African races (except the 
Egyptians). In making their bread (teff), they always 
include a sauce of red pepper to render it sapid. 

The Kabyles of North Africa live chiefly on onions, 
cucumbers, gourds, and water-melons, and they are 
especially fond also of a small wild artichoke. 

The Moors of Morocco are people of very ancient 
civilization, but nevertheless their mode of life is con- 
siderably simpler than ours, especially among the poorer 


classes. Kesk'soo, prepared from semolina, is the 
national dish ; zumetah (parched flour) and vermicelli 
are also used for making cakes ; very hard, doughnuts, 
flavoured with anise and caraway seeds, and called 
" fikaks," are commonly eaten. In addition, rancid 
butter, honey, dates, raisins, and large quantities of 
ripe melons and black figs form an important part of the 
food. " Kabab," made from chopped-up and seasoned 
meat, partially cooked is a very favourite dish ; salt 
is used extensively. Various kinds of confectionery 
are largely eaten, so that it is not surprising to know 
that the native " doctors " are acquainted with, and 
use three different instruments for, the extraction of 
teeth — namely, a native instrument which is " a sort of 
exaggerated corkscrew without a point," and also keys 
of French and English pattern. The possible presence 
of diseased teeth and the value set upon good teeth are 
shown by the fact of slave-dealers always examining the 
teeth and gums of slaves before purchasing. 

Australian and Tasmanian Aborigines. — Both of 
these races were nomadic, and lived largely on flesh food, 
such as insects, fish, birds, reptiles, and very many mar- 
supials. Various roots, fruit, honey, and the gums of 
certain trees, were also articles of diet. (Incidence of 
caries — Australians, 20-5 per cent. ; Tasmanians, 27 per 

Probably altogether they employed some three hun- 
dred different kinds of vegetable or fruit food, but no 
crops were cultivated in the ordinary sense of the word. 
Yams, nardoo, and bulrush-root were staple foods in 
many districts. The former two were made into cakes, 
and the latter is said to have occupied (he position that 
bread does to the European ; but it was very coarse, and 
the fibrous parts were spat out after chewing. Meat was 
frequently flavoured with the sweet secretion from a 
species of Psylla. 

A fermented liquor was prepared from the fruit of the 
pandanus. There are two things, however, which 


operated adversely in the diet of the Australian : firstly. 
his practice of eating clay after meals, and of mixing 
earth with yams before eating them ; and. secondly, 
his frequent difficulty in obtaining water, owing to 
periods of drought, or to his nomadic habit and the con- 
sequent necessity of passing over arid areas. The 
Tasmanians were not cannibals, but the Australians 
were ; and in many parts human flesh was consumed by 
both sexes and all classes, and sometimes one child of 
a family would be killed and given to another child to 
eat in order to strengthen it. 

The Ixhabitaxts of Ixdia. — The races, tribes, and 
castes, of India are so numerous that it is impossible 
to give any concise and accurate description of a diet 
which will apply to all. Rice is the staple food near the 
coast, millet in the Central Provinces, and wheat in the 
Punjab and North- West. In all cases the cereal is 
served in a variety of ways, usually retains some of the 
husk, and is seasoned with herbs or spices, the Indians 
being, of course, extremely fond of the latter. Eggs, 
milk, fruit (ginger, plantains, citrons, gourds, pumpkins, 
and in some parts oranges and lemons), and salt, also 
form a regular part of meals in most instances. In 
some parts (Khondistan) " butter " is made from two 
varieties of sinapis. Fish is abundantly eaten on the 
coast, but not in the interior, the art of angling not being 

Among many of the tribes of Northern India, the 
women collect considerable amounts of wild vegetable 
food with " digging spuds." Poisonous tubers are 
soaked in water to render them innocuous. The fruit 
of the Mohwa furnishes the food of the poorer classes for 
several months, and is usually eaten with Sal seeds or 
the leaves of various jungle plants, together with a little 
rice. The seeds of many wild grasses and bamboos, and 
the leaves of leguminous plants, form, indeed, a very 
important part of their food. 

The Todas, in Southern India, exist at the present 


time chiefly on milk, butter-milk, ghi grain, rice, and 
sugar ; but from their own statements they formerly 
lived on roots, herbs, honey, and fruit. The flesh of the 
calf is eaten only three times a year, but that of the 
sambhar may be partaken of at any time when an 
animal happens to be killed. During pregnancy the 
women drink the juice of the tamarind, which is markedly 
acid, but pleasant. 

Japanese. — The principal food is rice, also buck- 
wheat, wheat, barley, taro. and yams. A seasoning of 
some sort is used with every meal, usually either a white 
radish or the fruit of the egg-plant. The fruits of the 
kaki and biwa are largely eaten, as also are cucumbers, 
water-melons, and parts of the chrysanthemum flower. 
Meat is a rare delicacy. 

Chinese. — The staple food of all Chinese is rice ; it is 
served in a variety of forms, but is to European taste 
always " underdone." In addition, taro and sweet 
potato are largely eaten, and, of course, the Chinaman 
is proverbially a past-master in the art of cultivating 
" vegetables," which form an important part of the 
national menu. The Chinese are almost vegetarians 
by force of circumstances, and not so much by choice. 
Fish, salt and fresh, duck, and pig, are the chief articles 
of flesh food, and in this order of frequency, pig being 
consumed by the middle class and poorer Chinese on 
festive occasions only. A little mutton and beef is 
eaten in Northern China. Fruit is abundant in most 
parts of China, especially the south, but near the large 
towns and ports it is sold for export rather than eaten. 

Missionaries are of the opinion that the Chinese, in 
the country districts at least, have " most excellent 

Persians. — There are three national dishes : chillau, 
boiled rice with a little grease ; pillau, boiled rice with 
lamb; and ash, rice stewed with vegetables and fruit. 
Sherbet, the national drink, is made from iced water and 
fruit juices and essences. 


General Remarks and Conclusions. 

The incidence of caries in these races varies consider- 
ably — according to Mummery's figures, from 14 to 
20-8 per cent, (of individuals) ; and according to Patrick, 
from 2-064 t0 5*804 per cent, (of the total number of 
teeth). The latter figures are really the more important, 
since they give a more correct estimation of the extent 
of caries in any race. Now, as we have seen (pp. 9. 10). 
even the highest of these figures is incomparably lower 
than those obtaining amongst civilized races at the 
present time. So that we may group all the " natural " 
races together, and endeavour to ascertain whether 
there is anything common to their several dietaries 
which would explain their relative immunity to caries. 
Mummery and Miller believed that a larger consumption 
of meat explained the difference. This theory, how- 
ever, although a factor, must per se fall to the ground, 
since both Mummery's and Patrick's figures (see pp. 9-12) 
show that several meat-eating races have a higher 
incidence of caries than non-meat-eating. Also it is of 
the very highest significance that in Patrick's list the 
great rice-eating, almost vegetarian races of South- 
Eastern Asia should show the least incidence of caries : 
out of 2,000 teeth, only 2 per cent, were carious. 

Again, many of the people showing the highest inci- 
dence of caries (the colonials of Australia and New 
Zealand) consume enormous quantities of meat — 
namely, 240 and 250 pounds per head per annum 
respectively — yet the number of individuals affected by 
dental caries is estimated to be from 90 to 95 per 
cent, (by the Australian and New Zealand Dental 
Associations) . 

Therefore it is obvious that upon these considerations 
alone a large consumption of meat does not confer even 
a relative immunity. 

From this investigation several things stand out 
clearly: That the diet of all "natural" races and of 


those relatively immune to caries is essentially a varied 
one, and that although certain articles form the staple 
food over certain large areas, yet they in no case form 
the sole food of any race. 

There re, then, two general principles to be found 
running through the dietaries of all the natural races. 
They are — firstly, variety, and, secondly, sapidity. 

This inquiry was undertaken quite impartially, and it 
was not anticipated that the results would so amply 
bear out the previous investigations. The same con- 
clusions are made by Ratzel, an eminent authority on 
ethnology, but who had no reason to pay any particular 
attention to any one feature of the foods of such races ; 
yet, summing up the characteristics of the partially 
" cultured " people (Chinese, Japanese, Hindoos, Arabs), 
he says : " Variety of food is great, and the sense of taste 
appeals at a very early stage." 

The constant inclusion of articles in the food which 
have a direct stimulating effect upon the salivary glands 
is the one and only link which connects up all the races 
showing a relative immunity to caries. It is common 
alike to dwellers in the Arctic and Equatorial regions, it 
is found in meat-eating and in vegetarian tribes, it is 
present in both low and high types of uncivilized man. 

Further, it will have been noticed that although a 
variety of sapid substances are used, yet the ones most 
frequently recurring are acid in reaction, chiefly fruits 
and berries; and, as has been previously shown, these 
are the very stimulants which produce the most profuse 
and the most alkaline flow of saliva, and to this latter I 
think we are justified in ascribing the relative immunity 
found in the races which have been considered. Only 
on such a basis can the order of incidence in Patrick's 
figures be explained. 

In Southern Asiatics the percentage is least, and these 
are the people who have fruit in abundance, and use it 
as an ordinary article of food, and not merely a luxury 
at their meals. The Egyptians and Africans come next, 


including races which employ both fruit and salt largely 
(and also artificial prophylaxis). Polynesians and Aus- 
tralians are next, the percentage doubtless being raised 
considerably by the inclusion of the nomadic Australians. 

Central Americans follow, whose salivary stimulants 
are mostly sweet-acid, but whose comparatively higher 
incidence may be due to their consumption of cassava, 
which is " dry, tasteless stuff like sawdust." 

North Americans and Esquimaux are grouped next, 
although these people are amongst the largest meat- 
consumers. They both eat fruit and berries (and the 
Indians sugar-pine), but the amount must of necessity, 
owing to climatic conditions, be comparatively smaller. 

The highest incidence of carious teeth falls to the 
South Americans, including the Guachos, whose diet is 
mainly meat, and the Fuegians, who consume fish and 
fungus largely. The relatively higher incidence is also 
possibly caused by the inclusion of many earth-eating 
tribes, by the consumption of cassava bread, and by the 
general laziness of the Indians, who strongly " object " 
to cultivation. This, also, is one of the very few countries 
where salt was not used at all by the natives to increase 
the sapidity of their food. 

Totemism and Taboos. — In probably the greater 
number of natural races of mankind, food restrictions of 
one kind or another are enforced. In many cases this 
is due to totemism. An individual has a certain object 
for his " totem " ; this is always some well-known 
animal, plant, or natural feature of the landscape. 
When the totem is an animal or plant, it becomes pro- 
hibited as an article of food. (There are a few abnormal 
exceptions to this rule, but they are unimportant.) 
The interesting feature from the present point of view 
is that the great majority of totems appear to be animals, 
and this, therefore, would tend to restrict the consump- 
tion of animal food. The fact, too, that the totems of 
individuals of a tribe or family are not the same — in 
fact, in many cases are necessarily diverse — would 


further tend to restrict animal food. For instance, 
there mig-ht be six different animal totems in a family 
of seven or nine, so that whichever of those six animals 
happened to be for dinner, certain members of the family 
would be unable to partake of it. Other food restric- 
tions are related to sacred rites and seasons, or are en- 
forced at the period of puberty or afterwards for sup- 
posed sexual reasons. In these cases, also, the prohibi- 
tions relate chiefly to animal food. For instance, in 
certain Australian tribes there are thirteen different 
kinds of animal food which a boy may not eat before 
puberty, and eleven kinds which a girl may not eat 
until she becomes a mother. Amongst certain Melan- 
esian tribes no man until past middle age is allowed to 
eat dog, turtle, or six particular species of fish, and no 
woman may ever eat the two former; whilst in some 
places only middle-aged men may eat pig. These latter 
prohibitions are enjoined because the consumption of 
such animals is supposed to create a dislike by the 
opposite sex. In many instances animal food is taboo 
to one or both parents for a variable period after a child 
is born ; in the case of the Jakun, until the little one has 
acquired the use of its legs. 

In various countries, too, where cannibalism was 
practised human flesh was generally taboo for women, 
and not infrequently also that of certain animals, such 
as the dog. 

Attrition of Teeth in Native Races. — Nearly all races 
which are comparatively immune to caries show marked 
attrition of the teeth. It has been assumed that this 
must have been due to an excess of coarse or gritty 
material in the food ; but, as we have seen, this cannot 
be held to have been anything like sufficient in amount, 
since nearly all native races are most careful, in the 
preparation of their food, to eliminate all the obviously 
coarse particles and to cook it thoroughly. It is far 
more probable that the attrition is due to the mechanical 
effect of finer fibrous partides, combined with the con- 


stant action of the acids of fruits and berries. In fact, this 
" attrition " is to be regarded as in every way analogous 
to the " wasting " produced experimentally by Miller 
upon the labial surfaces of teeth by the combined action 
of acids and tooth-brush, and simulating erosion cavities. 
A similar condition of attrition or " wasting " of the 
occlusal surfaces of the teeth is seen in people of gouty 
diathesis, and, as is well known, a majority of such 
people are bons vivants, and as a rule have a preference for 
acid beverages (such as port wine) ; but it cannot be 
claimed that their dietarv is gritty or coarser than that 
of members of the same household who do not suffer 
from gout or attrition of the teeth. Undoubtedly, also, 
the musculature is more vigorous in native races and 
gouty individuals, and the " force " of mastication there- 
fore greater ; thus the acid and fine fibrous particles are 
aided in wearing down the cusps of the teeth. 


Bancroft : Native Races of the Pacific States of North 

Brown. J. M. : Maori and Polynesian. 
Crooke : Natives of Northern India. 
Guppy : The Solomon Islanders. 

Haddon : Head Hunters. Black, White, and Brown. 
Hill-Tout : British North America. 

Howitt. A. W. : Native Tribes of South-East Australia. 
Lloyd, A. B. : In Dwarf Land and Cannibal Country. 
Meakin : Life in Morocco. 

Pratt : Two Years among New Guinea Cannibals. 
Ratzel : The History of Mankind. 
Rivers : The Todas. 

Seligmann : The Melanesians of New Guinea. 
Skeat and Blagden : Pagan Races of the Malay Peninsula. 
Spencer and Gillen : Native Races of Central Australia. 
Taylor : Early History of Mankind. 
Thomas. N. W. : Natives of Australia. 
Tregear : The Maori Race. 
Werner. A.: The Natives of British Central Africa. 

Various Communications to the New Zealand Institute. 



Attention has been directed earlier to the general 
" softness " which characterizes modern diets, resulting 
in a lack of sufficient stimulus to the jaw-bones — there- 
fore in a crowded and irregular state of the teeth, and 
hence a predisposition to caries. The elimination of all 
fibrous elements from food, too, probably tends, as 
Wallace* has pointed out, to the increased lodgeabilit}' 
of foodstuffs, by robbing them of their detergent action 
upon the teeth. But, as has been shown, the inclusion of a 
large element of cellulose in foodstuffs does not of necessity 
prevent them from lodging and undergoing fermentation. 

It does in some cases reduce the acid production, 
but the reduction bears no relationship to the amount 
of cellulose present. 

There is another characteristic, however, of our 
modern dietaries which has been overlooked. I refer 
to its comparative non-sapidity, its usual neutral or 
alkaline reaction, and its general uniformity, all of which 
are properties which have been shown to be incapable 
of reflexly exciting a sufficient secretion of saliva to keep 
the mouth free by natural means from fermentation. 

One only has to reflect for a short time, to come to 
the conclusion that the substances of which we consume 
most are those which have the least taste. In fact, 
paradoxical as it may seem, modern communities have 
acquired or developed a " taste " for tasteless things. 
This " taste " is not evolved ; it is, I believe, acquired 

* "The Physiology of Mastication," London, 1903. 


by a process of training and education on the part of 
each individual. Compare the natural uneducated 
" tastes " of a child with those of an adult. The child 
will in all cases select the most sapid substances, and 
eschew the insipid ones as a rule, much to the horror of 
its parents. Moreover, if a child be allowed to exercise 
its own uninfluenced choice, it will almost invariably be 
in the direction of a substance having an acid reaction. 
It is the parents who, by constant training and insisting 
upon other articles of food being eaten, eventually pro- 
duce in the child a tolerance of insipid substances.* 
This is done in all good faith by the parents for the 
child's health ; it is prevented from eating substances 
which they know would in themselves produce gastralgia 
and dyspepsia. But it is entirely a gratuitous assump- 
tion that a like result would be produced in a healthy 
child by the consumption of such articles in amount 
proportionate to its age. 

The digestive secretions of the parent have become 
vitiated and depressed through long years of depression 
or maltreatment. A normal child's are in a natural 
condition, and adapted to deal with food in a natural 
form. I have frequently noted that very young children 
will deal with acid substances like fruit and salad 
quite successfully, yet a proportionate amount consumed 
by adults causes considerable discomfort. 

It is within the knowledge of all, too, what enormous 
proportions of comparatively sour fruit may be consumed 
by the schoolboy with impunity. 

If the salivary glands are in a state of proper develop- 
ment and excitability, all the ordinary natural acids 
should be rapidly neutralized — if not before being swal- 
lowed, at least almost immediately afterwards, by the 
increased after-flow of a highly alkaline saliva. Not 
only is the " education " of the reflex salivary mechanism 
thus neglected, but salivary secretion is actually de- 

* The following sentence in a child's story-book unconsciously 
reflects a real physiological principle : " It was not so much the 
cake as the cherries in the cake that Norah liked." 


pressed by the very much increased consumption of such 
articles as tea and meat. There is no doubt that children 
at the present time consume enormously more of these 
salivary depressants than they did a hundred and fifty 
years ago, when teeth were comparatively healthy. 

From a dental point of view alone, neither tea nor 
meat could exert any harmful action by themselves, of 
course ; but it is when they are taken in conjunction with 
soft, adhesive, insipid carbohydrates, as they usually 
are, that the harm results : even the feeble natural 
protection evoked by the latter is still further decreased. 

Compare the dietetic conditions in England, say. one 
hundred or two hundred years ago. when caries was 
quite a spasmodic disease, with those obtaining to-day. 
Then there were no elaborate roller mills for the ultra- 
refinement of flour, bread was very largely " home- 
made " from flour ground between stone rollers ; then 
there was no wholesale importation of meat from abroad, 
there were no enormous biscuit and chocolate factories 
pouring out hundreds of tons of tooth-destroying 
material every year, tea and sugar were both articles of 
luxury and very dear. 

The practically universal drink at all meals was wine, 
French and Spanish being drunk by the upper classes, 
and English wine — i.e., cider — being the drink of the 
middle and lower classes ; and these, of course, were 
active salivary stimulants. Pepys wrote in 1660 : " I did 
send for a cup of tee (a China drink) . of which I had never 
drank before." England now receives from India and 
Ceylon alone 300,000,000 pounds per annum, and the con- 
sumption per head is between 5 and 6 pounds per annum. 

The manufacture and consumption of confectionery 
has developed enormously of recent years, and in this 
easily fermentable sugars are largely used, not the least 
of which is honey. The production of honey for this 
purpose is conservatively estimated at 300,000 tons 
per annum. Again, honey by itself would not be any- 
thing like so harmful as it is when incorporated with 
finely pulverized and cooked starches. 



The total consumption of sugar per head for the United 
Kingdom is estimated at 77-83 pounds per annum, and, 
seeing that nearly the whole of this probably is uncombined 
with an acid, it all has a potential for initiating caries. 

The method of making bread nowadays by chemical 
aeration conduces also to caries. In the old-fashioned 
method yeast more or less pure was used in the " leaven- 
ing " process, and also a not inconsiderable amount of 
salt (as is the custom in Scotland at the present time), 
the result being that the bread had a distinctive flavour 
of salt and a just appreciable aciditj^ due to the presence 
of acetic and lactic acids. Now, however, since " aera- 
tion " is produced by the action of acids on carbonate of 
soda, and since excess of the latter is always added to pre- 
vent sour taste, the resulting reaction is always alkaline, 
and therefore the bread is a salivary depressant. 

In order to have some definite facts as to the average 
food of a modern civilized community, I collected the 
detailed dietaries of 1.500 public school children on one 
day. The age of the children varied from ten to fourteen 
years. The district was one in which there is prac- 
tically no poverty, in which, too, the living is known to be 
good amongst all classes, yet it is one, also, in which caries 
is known to be present in over 90 per cent, of the children. 

The following tables give in concise form some of the 
results of the inquiry ; they are self-explanatory : 






Percentage of Meals 

Article of Diet. 

in which it formed 
a Part. 

Bread and butter 








Bacon (or meat) 




Cake or biscuit 











Percentage of Meal 

Article of Diet. 

in which it formed 
a Part. 











Lemonade . . 





Pudding or pie 


Vegetables . . 


Bread and butter 

40- 1 

Biscuit or cake 

1 9-6 
















Lemonade . . 







Scones, cakes, or bis 



Bread and butter 




Vegetables . . 


Pudding or pie 

























Lemonade . . 




2 74 




Percentage of 

Article of Diet. 

Children who took 
it for Supper. 

Bread and butter 

I 5 -u 


I 4 .8 


13 -o 

Chocolate . . 






Fish and potatoes 

I -J 
















Lemonade . . 


In cases where no supper was taken, the last thing 
eaten at tea-time is recorded in the following table : 


. 16-80 

per cent 

Bread and butter 

• 1 . ; • ; 



5 MO 

t , 

Bread and jam 


, , 




Meat and potatoes 












It cannot be suggested that these tables do not show 
an extremely liberal dietary : it is possible that in some 
cases a little more than the truth was told, but for the 
wist majority of the cases I am satisfied that these 
tables represent faithfully the dietary of the district. 
Such diets might be criticized from other points of view 
than the solely dental, especially bearing in mind that 
it is the food of children which is being considered. 

Note, for instance, the enormous proportions of meat 
and tea which are consumed, loading up the systems of 
the children with alkaloid and extractive stimulants. 


From a dental point of view, the diet may be very 
briefly summed up as being salivary depressant and of 
high acid potential. 

A most remarkable similarity will be noted between 
the order in which the articles of diet are arranged in 
these tables and the order previously noted of their 
capability of acid production. They are also practically 
in inverse order to their power as salivary stimulants. 

If nothing were known about the teeth of these 
children, it could be said with absolute certainty from 
these data that they would be found to be in an extremely 
bad condition. This, as has already been indicated, 
is so ; moreover, speaking from a considerable experi- 
ence in examining the teeth of the children of this 
district, the incidence of caries in each mouth is appal- 
lingly high, so much so as to constitute a disgrace to any 
well-to-do civilized community. 

One of the points of most importance is the food last 
eaten during the day, and therefore, in the majority of 
cases, debris of which would remain to be fermented 
during the night. 

It is seen that bread and butter, cake, biscuit, and 
chocolate, are the articles which are last consumed in 
the great majority of cases — articles which adhere 
strongly to the teeth, form the greatest amount of acid, 
and produce the least flow of saliva. 

It is, again, one of the most significant facts brought 
out by this inquiry, that not one child in fifteen hundred 
had fruit of any kind last thing at night, and that only 
0-8 per cent, had fruit as the last thing at tea-time. 

In view of the fact that fruit has been shown to be 
one of the best detergents and excitants of the solvent 
and neutralizing powers of saliva, its practically complete 
absence here cannot be regarded as other than one of 
the greatest causes of the prevalence of caries. 

Although, naturally, diets vary in different localities 
and countries, and vary also amongst different classes 
in the same districts, yet it probably would not be 


wrong to take the foregoing tables as representing an 
average dietary of modern civilization, erring, probably . 
on the side of liberality ; but. still, the proportions of 
substances to each other for various meals (excepting, 
perhaps, meat and tea) would, I think, practically hold 
good. We may therefore conclude that the dietary 
of civilized communities at the present time errs seriously 
in the direction of being too soft, of having too high an 
acid potential, of being not sufficiently stimulating to 
the salivary glands and not sufficiently detergent. 

In considering how such a dietary may be corrected, 
social and economic conditions have to be borne in mind ; 
it is neither possible nor desirable that any sudden or 
drastic change should be made. Conditions must be 
accepted as they are found, and an attempt made to 
improve them. 

It is impossible, for instance, under modern conditions 
to ban absolutely all soft and fermentable carbohydrates. 
Improvement in this direction may come in time, but 
it will be essentially a slow and gradual process, depend- 
ing upon the rapidity with which people are educated 
to demand such an alteration. 

Sufficient has, however, been said to show how the 
majority of food substances of high acid potential may 
be rendered practically innocuous. 

It has been shown that by the combination of strong 
salivary stimulants with such substances, either in a 
mixture or, much better, in sequence, the acid produc- 
tion may be reduced to a minimum or entirely negatived. 

What is therefore to be advocated is that all meals 
should contain a fair proportion of salivary excitants, 
and, more important still, should both commence and end 
with some article of diet having an acid reaction. 

This does not of necessity imply a " vegetarian " 
diet ; in fact, many " vegetarian " meals are distinctly 
conducive to caries on account of their soft, pappy, and 
adhesive nature. 

The only meal in which the principle of salivary 


stimulation is usually correctly observed at the present 
time is a dinner commencing with hors d'ceuvre, and 
terminating with fruit as dessert. 

A similar arrangement, however, can be quite easily 
arranged for all other meals. When garden fruit and 
vegetables, particularly the " salad " variety, are in 
season, this should present no difficulty whatever, and 
the length of " season " is constantly being lengthened 
by the importation of fruit and vegetables from warmer 
climates ; in fact, at all seasons of the year now, and 
practically everywhere, some fresh fruit at least is 

For breakfast, porridge with salt may form the initial 
stimulant. This may be followed by anything else 
customary to the individual, such as fish, bacon, bread 
and butter, and marmalade or jam ; the latter should 
have a distinctly acid flavour, and should not be merely 
syrup flavoured with fruit-juice, as too many of 
the factory-made articles are. The meal should be 
concluded with some form of fresh fruit — orange, apple, 
banana, pineapple, pears, plums, etc. — preferably raw, 
but they may be " stewed." 

For luncheon or the midday meal, the initial stimulus 
may be some modified form of hors d'ceuvre, such as a 
radish or a small portion of some acid fruit. 

With meat some form of sauce may be taken ; such 
things, being nearly all acid, serve as excellent salivary 
stimulants. (There is no objection to children taking 
small quantities of these sauces. I have never seen any 
ill results follow.) The meal may be concluded with 
stewed fruit, fruit pudding or pie, provided that in the 
latter the fruit predominates, and not the starchy 
element, and that it is not made too sweet. " Salad " 
should, of course, be taken wherever possible, but its 
good effect may be entirely neutralized by its being fol- 
lowed, as it too often is, by a biscuit and coffee or some 
form of confectionery and tea. 

Tea, especially when it is the last meal of the day. is 


the one most responsible for the production of caries. 
It almost invariably ends with cake and a second or 
third cup of tea, containing probably, in the vast 
majority of cases, a high percentage of tannin. Thus 
absolutely ideal conditions are brought about for acid 
fermentation to take place in the mouth. There are a 
number of salivary stimulants which may be included 
in this meal, such as tomato, cucumber, cress, sardines, 
shrimps, or fruit sandwiches. Fruit salad or any fruit 
in season should terminate the meal. 

Last thing at night, children (and adults too) should 
always eat a small portion of some detergent and acid 
fruit, such as orange, apple, pear, or pineapple. 

Taken in such a manner, the total amount of fruit 
and vegetable need not be large, and in no case should 
such a dietary be commenced suddenly; it should, 
especially in those who have been unaccustomed to the 
inclusion of fruit and salad in their dietary, be worked 
up to gradually, commencing with one meal a day; then, 
after a week or so, two meals may be terminated with 
" acids," and finally the principle may be extended to 
all meals. 

Should any intestinal irritation be set up, the inclusion 
of boiled milk in the dietary will correct it ; this I have 
found to be but very occasionally necessary, and only 
in the initial stages. 

The much-dreaded bugbear " diarrhcea " is much 
more likely to be caused by eating fruit in an unclean 
condition than to be due to the mechanical or chemical 
action of the fruit on the bowel. All fruit, therefore, 
especially that of unknown source, should be well 
washed or have the skin removed before being eaten. 
The only effect of fruit taken regularly and in such 
moderate quantities is to insure a full and regular 
action of the bowels. 

In special cases the reaction and amount of saliva 
should be estimated during the change, to see that the 
desired result is being produced ; and when the maximum 


amount and alkalinity per minute have been reached, any 
increase in the acidity of the dietary should be stopped, 
and it may even be decreased a little. 

The difficulty, in many cases, of adopting such a dietary 
may be on account of expense and inaccessibility of 
fresh fruit and vegetables. Tinned fruits are, however, 
now everywhere available at moderate cost ; and these, 
especially pears, pineapple, and apricots, may be substi- 
tuted, not with advantage, but as being better than 

In respect to fluids, children particularly should never 
drink tea, and the less it is consumed by adults the 
better, even from a dental point of view alone. 

Milk, water, home-made lemonade, and weak lime- 
juice, are the beverages suited for children. Lemonade 
should not be too strong, and should contain a sufficiency, 
but not an excess, of sugar; that is to say, the acid 
should be quite appreciable to the child, and should be 
sufficient to precipitate the mucin and prevent the 
sugar from being fixed to the teeth. 

If similar beverages were more consumed by adults, 
it would, I think, largely lessen the craving for tea and 
sweetmeats so prevalent at the present time. 

As regards sweets, all are good in that they are salivary 
stimulants, and all are bad in that they are readily 
fermentable ; and as a general rule it may be said that 
the ill effects quite outweigh the good effect. They all 
(practically) leave sugar behind in the mouth to be 
transformed into lactic acid- — -chocolates and caramels 
most, and hard-boiled sweets like toffee least. The old- 
fashioned " acid drops " are possibly the least harmful. 
Children should, however, be encouraged to spend their 
pocket-money on fruit rather than on sweets, and on 
biscuits least of all. Almost all children prefer fruit to 
sweets if they are allowed to exercise their choice. 
Of the 1,500 children whose dietaries I examined, 
90-35 per cent, said they preferred fruit to sweets, and 
only 9-65 per cent, preferred sweets ; yet the amount 


of sweets consumed by these children was enormous, 
and the amount of fruit a minimum. I think there is no 
doubt that a growing child can obtain all the sugar it 
needs for its muscles, fat, and heat development, from 
consumption of it in a natural form — i.e., as found in fruit 
and some vegetables. 

Bunge * has called attention to the danger of the 
great increase in the consumption of pure sugar in 
recent times, pointing out that it must diminish the 
amount of vegetable foods in the diet, thus leading to a 
loss in the supply of calcium, iron, fluorine, and other 
mineral ingredients to the blood. Hutchison is also 
of the opinion that it may be connected with the 
increased commonness of diabetes. 

It is commonly affirmed in textbooks that one of the 
articles which have been quoted as salivary stimulants — 
i.e., cider — destroys the teeth. With this the author 
cannot agree, having had considerable experience of 
the teeth of the inhabitants of one of our cider counties, 
and also of those of other counties and countries. The 
difference between dentures from this county, and those 
from an adjoining county where mining was carried on, 
and fruit and cider were not available, was always most 
marked and obvious ; and whenever the mining com- 
munity makes an excursion into the cider county, 
their avidity for fruit is, to say the least, very 

It has been stated that the consumption of large 
quantities of grapes in those patients undergoing a 
"grape cure " has bad effects upon the teeth. I have 
no knowledge of this ; but if so. it is probably attribut- 
able either to the grapes being too ripe and hence 
acting, as has been shown, as very feeble salivary stimu- 
lants, or, if not too ripe, to the constant presence of too 
much acid in the mouth proving more than the saliva 
can neutralize ; possibly the glands get overworked, and 
do not have time to recuperate. 

* Quoted by R. Hutchison, " Food and Dietetics," p. 280. 


Black* some years ago came to the conclusion, after 
" a hasty examination " of dried skulls, that there was 
a connection between immunity to caries and sour-fruit 
eating, but apparently abandoned or did not follow up 
his conclusion ; and Leon Williams f states that the 
Sicilians, who are large consumers of lemons, are par- 
ticularly free from caries. 

Note on the Soured Milk Treatment. 

However beneficial this treatment may be for other 
portions of the alimentary tract, there can be no doubt 
that as a general rule it must be harmful to important 
organs of the first part of the tract — i.e., the teeth. 
Not because the milk is sour — in that respect it can be 
only beneficial — but because a large number of lactic 
acid organisms are introduced into the mouth, and these 
of a variety specially selected on account of their ability 
to form a maximum amount of acid. The following tests 
with soured milk give examples of what may happen : 

Two persons, A and B, drank ordinary milk, and 
then each insalivated 2 grammes of bread ; this was 
incubated for forty-eight hours, and the acid formation 
estimated — 

A = 2-83 units (I NaOH). 
B = 2-8 

Milk which had been infected with lactic acid bacilli 
(fermenlactyl) for eighteen hours at body temperature 
was then drunk, and 2 grammes of bread again insali- 
vated by each. In forty-eight hours the acid production 
was — ■ 

A=4 - 6 units. 

B=47 " 

This considerable increase in both cases could only 
have been due to a considerable increase in the initial 

* " American System of Dentistry," p. 730. 

f Quoted by Goadby, " Mycology of the Mouth," p. 139. 


number of organisms present in the mixture, and there is 
no reason to doubt that the figures represent the pro- 
portionate tendency to tooth destruction in both cases. 

Both of the above individuals were susceptible to 
caries ; a similar test was made with an immune person : 

After ordinary milk, the bread yielded in forty-eight 
hours i '4 acid units. 

After soured milk the bread yielded in forty-eight 
hours 1*2 acid units. 

The difference between this and the two former tests 
is very marked ; not only is the acid protection from the 
control only one-half of what it was from the susceptibles, 
but also the amount of acid produced from the bread 
masticated after soured milk was less than the control. 
The results are to be explained entirely, I think, by the 
increased neutralization by the saliva of the immune. 
It therefore seems clear that in the average individual — 
i.e., one susceptible to caries — soured milk may prove to 
be very harmful to the teeth. In order to combat this 
the teeth should be cleaned, and a salivary stimulant 
used immediately after taking the milk (or powder). To 
expect to remove the introduced organisms by rinsing 
the mouth out with water for half a minute or so would 
be futile. I would suggest the eating of a piece of orange 
as one of the simplest and best prophylactic measures 
which could possibly be adopted. 



There can be no doubt that ignorance is largely 
responsible for the present widespread prevalence of 
dental caries — ignorance of the cause, ignorance of a 
remedy, and ignorance of the gravity of the condition 
and the secondary consequences. Ignorance chiefly on 
the part of the general public, but not entirely; alas! 
also, to a greater or less extent, on the part of physicians, 
surgeons — and dental surgeons, too. 

It is clear that, in order to obtain any appreciable 
diminution of the incidence of a disease which is afflicting 
over 90 per cent, of the population, knowledge of the 
cause and seriousness of the conditions cannot be too 
widely disseminated, nor the general adoption of the 
utmost prophylactic measures available be too insistently 

There are three classes who have the power of pro- 
pagating this knowledge in especial degree. They are 
the teachers in primary schools, medical men, and 

1. The Teachers in Primary Schools. 

Educationists are coming more and more to recog- 
nize the truth of the well-worn adage, Mens sana in 
cor pore sano, and are devoting more time and attention 
to the attainment of that end. Hygiene and physical 
drill are taught, cooking is taught, and free meals are 
provided. But these will benefit nothing if the child is 
suffering from septic absorption arising from diseased 



teeth. Wallis* has found that the children with the most 
marked oral sepsis were always at the bottom of their 
class. It is therefore to the interest of education, and of 
those teachers who desire to see the mental capacity of 
their pupils developed to the greatest extent — under 
the best conditions for their profiting thereby — that 
considerable attention should be paid to the prevention 
of dental caries. 

The mere examination of the children occasionally by 
a medical man or a dentist, and being advised that their 
teeth require treating, is utterly insufficient ; an occa- 
sional explanation, perhaps by the school medical officer 
or school dentist, of the means and necessitv of prophy- 
laxis, is likewise absolutely inadequate. What is neces- 
sary is persistent, regular, oft-repeated definite lessons 
in oral hygiene, and the only persons in a position to 
carry out such work are the teachers themselves. Such 
definite and regular lessons should be given to the 
children in each standard separately. The lessons should 
be graded according to the standard and understanding 
of the pupils. 

In order to stimulate the interest and make it a real 
" lesson " to the higher standards, it will be necessary to 
go into much more detail than would be possible or 
desirable for children in the lowest standards ; but no 
child should be too young to receive some definite 

Children should be made to realize the value, physio- 
logical and financial, of sound teeth. Reduced to its 
most sordid aspect, the loss of all tooth substance means 
the expenditure sooner or later of money, or its loss 
through incapacity. By ascertaining the average weight 
of teeth, it is estimated that each tooth is worth to its 
possessor the monetary value of an equal weight of 
gold at least ; that each part of a tooth dissolved by 
lactic acid is equal to so much gold taken out of the 

* Wallis : " The Necessity of Dental Clinics in Connection 
with Elementary Schools," British Dental Journal, 190S.. p. S61. 


individual's pocket — not voluntarily, but with absolute 
certainty, and involuntarily. 

Occasional lessons to a whole school on such a subject 
would not excite much attention on the part of the 
pupils, and in a few weeks at most all the details of the 
teaching would be quite forgotten. There should be at 
least one or two lessons given in each term in each 
standard ; and then by the time a child has passed 
through all the standards it may be hoped that some 
of the main principles of oral prophylaxis will have been 
really learnt, will be put into practice, and the effect 
last until such time as the child becomes in turn a 
parent ; for. after all. it is the parents who have the power 
and the will to largely reduce the prevalence of caries. 
But, of course, parents qua parents are difficult to 
reach by educational means ; it is therefore from the 
proper instruction of the potential parent that we have 
most to expect. 

In order that such work may be carried out, and in 
view of its national importance, the teachers must 
themselves first receive instruction. There should be 
appointed to all training colleges a dental surgeon, 
who should deliver a short course of six lectures annually 
to the students there being trained for the teaching 
profession, and a certificate of having attended such 
lectures to the satisfaction of the lecturer should be 
absolutely obligatory. Further, all dental associations 
should arrange for lectures to be delivered locallv to 
those teachers who have previously received no such 
instruction. (Such lectures should not be purely 
honorary, but should be sufficiently well paid ,to insure 
their being well prepared and well presented.^ 

For the purpose of instructing both pupils and 
teachers, diagrams — as many as possible — are a sine qua 
non. The visual centres of the average modern brain 
are far more retentive than the auditory, and every 
advantage should be taken of the fact. The diagrams 
should be simple and bold — should be diagrams, and not 


pictures, far less actual photomicrographs. It should 
be remembered that we are dealing with people un- 
trained in differentiating minute histological details, and 
what is required is that an impression should be created, 
and a lasting impression — such that a mental- picture of 
any important diagram could be visualized at any time. 
Stress is laid upon this point, because many of the 
diagrams intended for school use at the present time 
are far too complicated and technical for a lay mind, 
and for a child's grasp in particular. 

The teachers, also, of the cooking classes held for the 
senior girls in many schools should recognize that by 
their teaching they can accomplish much for the good or 
ill of the teeth of the people. There should be no diffi- 
culty at all in treating even simple and inexpensive 
dishes so that they may contain salivary stimulants, nor 
in arranging them in proper order, that the most fibrous 
and more acid constituents of a meal may come last. 
Much may here be done to educate the gustatory nerves, 
to cultivate in the children a taste for tasteful things 
(other than confectionery) ; to stimulate their interest 
in, and to point out the necessity of, as large a variety 
of fresh vegetables, salads, and fruits, as possible ; and, 
on the other hand, to teach them to avoid tasteless, soft, 
sticky, and simply sweet articles of diet, and so on. 

But here again, in order that the teacher might work 
rationally and enthusiastically, it would be necessary 
that she should first of all understand thoroughly the 
physiological principles underlying such measures, and 
should appreciate the urgency of their adoption. She 
should appreciate, too, that by stimulating the glosso- 
pharyngeal and lingual nerves, not only will the teeth 
be protected, but the gastric juice be psychically stimu- 
lated, and the meal therefore better digested. 

The students, therefore, in schools of cookery should 
receive instructions also in the cause and prevention of 
dental caries ; and the Board of Education authorities 
should recognize the importance of such knowledge, 


and the serious responsibility of teachers of cooking in 
disseminating knowledge which may be for good or for 
ill in the health of the nation. 

2. Medical Practitioners. 

Medicine and dentistry have been most closely 
associated since the very earliest times ; in fact, down 
to the seventeenth century dentistry was practised 
almost exclusively by physicians. Dentistry then began 
to be practised by men who had not been trained as 
physicians or surgeons, and their numbers have gradually 
increased from then until now. This is in itself a matter 
for regret, but what certainly is a matter for much more 
regret is that, correspondingly, interest in the teeth on 
the part of physicians and surgeons has gradually 
diminished, until it has fallen almost to zero. There 
is too great a tendency to regard the teeth as isolated 
parts of an organism, as organs which exist of themselves 
and for themselves, and are not intimately linked up in 
function with the rest of the body. It is not sufficiently 
recognized that the teeth are an integral and inseparable 
and most important part of the alimentary system, both 
from a physiological and pathological point of view. 
In consequence of this the amount of training and 
instruction a medical student obtains at the present time 
in the diseases of the teeth is almost negligible. The 
result is that a medical practitioner is, by overlooking 
the teeth, liable to overlook the origin of the disease he 
may be treating ; but this, serious as it may be, is not the 
most serious thing that results. A medical man has 
almost unrivalled opportunities for impressing upon 
parents the necessity for preservation of the teeth by 
dietetic and prophylactic means ; but if as a student he 
learnt nothing of dental physiology and pathology, nor 
of the treatment of diseases of the teeth, he is not in a 
position either to seize the opportunity or to act upon 
it. The advice of a medical man on the condition of 


a child's health is usually sought many years before the 
child is taken to a dentist, yet not perhaps before signs of 
dental caries have begun to manifest themselves ; and it 
is at this period that sound advice is so valuable, and 
its omission so far-reaching in its effects. There can be 
no doubt that the constant and systematic omission of 
reference to the teeth by general practitioners has had a 
great deal to do with the apathy with which the majority 
of the laity regard dental disease. The ordinary indi- 
vidual argues that if the condition of the teeth were 
important, or had any relationship to other diseases of 
the body, the doctor would have been sure to mention 
it. If on the other hand the doctor in examining his 
patient never omitted the teeth, and always upon 
finding signs of disease of those organs gave advice as 
to prophylactic treatment, and insisted as far as possible 
on this being carried out, how different in a very short 
time would be the opinion of the public as regards the 
importance of the preservation of healthy teeth ! 

In those cases in which some advice is given, it is 
usually " to clean the teeth " or " to visit the dentist" — 
quite sound in itself, but which, by falling far short of 
what is necessary, conveys an impression of unimpor- 
tance. Dental caries is, as we have seen, in a large 
measure due to errors of diet extending over the first 
twelve years of a child's life, and it is just during that 
period that the general practitioner's advice is frequently 
requested as to the suitability or otherwise of articles of 
diet ; or, at least, he has opportunities of pointing out 
authoritatively the deleterious effect of the common 
dietetic errors from a dental point of view. We cannot, 
therefore, avoid the inference that, if such had been the 
universal practice, the incidence of caries would not now 
be anything like so high. In order to avoid such a stigma 
in future, medical students must be instructed in the care 
of the teeth. A medical student, before he qualifies, 
should have some knowledge of what diet is beneficial 
and what deleterious to the teeth, and he should be 


taught to put this into practice. In doing so he will only 
be fulfilling the general principles of correct dietetics, for 
it might be stated in general terms that " what is best for 
the teeth is best for the rest of the alimentary system." 
He should also know something of how to aid natural 
resistance to caries by artificial prophylaxis ; he should 
be able to write suitable prescriptions for various mouth 
washes, dentifrices, etc., for varying conditions of the 
mouth ; he should be able to instruct parents in the care 
of their children's teeth. All this and more he should 

He is taught along similar lines with regard to the 
eye, the ear, and throat ; why, then, should the teeth 
and mouth be omitted ? He should, in fact, attend a 
short course (theoretical and practical) on stomatology, 
or diseases of the teeth and mouth, and having some 
precise knowledge of such matters he will no longer think 
them unimportant.* He will then be in a position to 
render valuable service to his patient ; to himself, in the 
saving of his time in the diagnosis and treatment of many 
cases ; and moreover, and above all, to the community 
as a whole, by directing attention to the necessity of 
adopting stringent but rational methods for the pre- 
vention of dental caries. 

3. Dentists. 

If, during the past one hundred years, half as much 
time, money, and brain power, had been spent in evolving 
means for the prevention of dental caries, as has been 
spent in the perfecting of ways and means for replacing 
artificially tissue lost by disease, there can be no doubt 
that the present condition of affairs would not have 
come about. In fact, it is probably not too much to say 
that the majority of the members of the dental pro- 

* Such a course need not add any_time to the curriculum. 
One hour a week during the final summer session can be found 
without difficulty, and, from personal experience, I find students 
are only too willing to attend such a class. 



fession have been content, not to treat the disease at all 
from a seriously preventive point of view, but merely 
to make good, as far as possible, the destruction produced 
during the progress of disease. 

Unfortunately, the training at most of our schools 
and hospitals must be blamed for this. If one may 
judge from personal experience, and from the amount 
of space devoted to prophylactic treatment in text- 
books, the extent of a student's teaching in this subject 
is somewhat limited. An examination of the six best- 
known textbooks on dentistry — three English, two 
American, and one German — shows that on an average 
o*i6 per cent, of a book is devoted to the preventive 
treatment of dental caries ; yet no one would suggest 
that this proportion in the least degree represents the 
importance of the subject. 

The dental student, whilst at hospital, should have 
full facilities and time for learning all that can be 
taught him in this branch of his work ; it should not 
be looked upon as a subject which can be " picked up " 
anyhow, or as one which it is not necessary to know 
much about before qualification, and which may then 
perhaps be relegated to the attention of a few " faddists." 
There should be special lectures by a suitable lecturer on 
preventive dentistry ; this should be supplemented by 
a practical laboratory class where experiments and 
observations bearing upon the prevention of caries could 
be made by students. The student would thus come 
to know the facts of the subject, instead of having a 
more or less empty belief in them only. Students 
should also attend a special clinic for the treatment 
of cases by prophylactic means. They should be taught 
to go into each individual case very thoroughly, to 
ascertain wherein lies the cause of caries in any particular 
case ; to find out which part of the line of defence has 
broken down or is too weak, or, on the other hand, 
what factors in the attacking forces are increased in 
amount or virulence. When this has been ascertained 


by means of accurate visual, chemical, and bacterio- 
logical observations, the student should be taught to 
outline a course of treatment for the patient — to draw 
up a dietary, and write prescriptions, and give instruc- 
tions for artificial prophylaxis, suitable to the case. 

There is one other matter in which the dental pro- 
fession and the teaching of dentistry in Great Britain 
lag behind. No provision is made in any of our 
hospitals, schools, or Universities, for the proper re- 
muneration of teachers of dentistry or dental subjects ; 
consequently, except in a few cases where special grants 
are made, no teacher of dentistry can possibly spend a 
great deal of his time in research work. In medicine full 
facilities are offered for research and progress in the treat- 
ment of a number of diseases, at Universities and hos- 
pitals — in dentistry practically none. There can be no 
doubt that until Universities and governing bodies recog- 
nize the importance of the subject, and create " chairs " 
whereby the holders may be justified in devoting the 
whole of their time, energy, and enthusiasm, to teaching 
and research work, the teaching will continue to be of a 
spasmodic and disconnected character. 



There can be no doubt that the gravity of the disease 
with which we are dealing is not recognized by the 
laity, and therefore not by Governments. The extent 
of the disease is beginning to impress itself upon authori- 
ties now that the examination and possible treatment 
of school-children is being undertaken at the public 
expense. So far, however, the cost involved in the 
treatment of dental caries by " fillings " on a universal 
scale has appeared to-be so great as to hinder any other 
than isolated efforts in this direction. But even now 
that it is beginning to dawn on authorities and public 
bodies that 90 per cent, of the children have carious 
teeth, the seriousness of what this means, the gravity 
of the ills to which the condition is precedent, is not in 
the slightest degree appreciated. 

It is perhaps agreed that " bad teeth cause indiges- 
tion," and that is as far as the sequence of events is 
followed. This is bad enough in itself, for how can it 
be hoped to rear a nation of mentally and physically 
strong individuals if, during the periods of growth and 
development, there is indigestion, and therefore non- 
assimilation of food ? Added to this is the slow, insidious, 
but nevertheless sure, chronic septicaemia, brought about 
by the constant ingestion of toxins, pus, and bacteria, 
from a mouth containing numerous suppurating foci. 
It must be recognized, too, by the public that anaemias 
of severe type are frequently induced in the same 
manner ; that tubercular glands of the neck, serious 



forms of Ludvig's angina, frequently fatal, are also 
caused by diseased teeth ; that malignant disease (cancer) 
of the jaws, tongue, and lips, often originates solely from 
diseased teeth, and from this cause alone a large number 
of lives is lost annually ; that a large number of dis- 
orders of the adjacent parts — i.e., muscles, bones, nose, 
eyes, and ears — are intimately associated with diseased 
teeth, either reflexly through the nerves or by direct 
extension of the morbid process ; that in conditions 
of unstable cerebral equilibrium the presence of 
diseased teeth is frequently sufficient to excite an 
attack of nervous disease, such as epilepsy, tic (spasms), 
hysteria, and some forms of insanity ; that, in addition 
to all these ills, of which large numbers of cases have 
been, and are constantly being, recorded, there is a 
chronic lassitude, lack of appetite, mild headache, con- 
stipation, and an inability to perform a normal amount 
of work, almost invariably associated with extensive 
dental disease. It is this relationship between cause 
and effect which requires to be driven home in the public 
mind. The disease itself is not always obvious, and the 
channels by which its effects spread are not recognized. 

If the disease were more obvious, there is no doubt 
that long ago the public mind would have been stirred, 
and legislation would have been passed to facilitate the 
checking of such universal suffering. Suppose, for 
instance, every alveolar abscess pointed on the face 
instead of in the mouth, the hideous disfigurement 
resulting therefrom would long ago have arrested 
attention ; yet probably in this case the harm to health 
would be infinitely less, because the products of disease 
would be to a certain extent outside the body, and not, 
therefore, absorbed into the system. 

Suppose a similar condition affected the finger-nails — 
suppose that 90 per cent, of the community went about 
with decayed or suppurating finger-nails — the idea 
would long ago have been so revolting that extensive 
measures would have been adopted for the suppression 


of such a disease ; yet the total systemic disorder and 
the annual loss of life would have been far less than it 
is from dental disease. 

The report of the Royal Commission on Physical 
Deterioration found that dental caries was a potent 
cause of physical deterioration, and Osier is of the 
opinion that in this respect the effect of dental disease 
is greater than that of alcohol. On humanitarian grounds 
alone, then, action is urgently required to suppress the 
advance of this most prevalent of all diseases. The 
principle has been recognized in nearly all communities 
now, that the Government is responsible in the main 
for the health of the nation ; and in cases of serious 
epidemics, of widespread toxic effects, of disease 
affecting large proportions of the people, legislation is 
provided enabling authorities to cope with the evil. 
Surely a disease affecting 90 per cent, of the population, 
and as far-reaching in its effects as this has been shown 
to be, is a national ill, and demands legislative measures. 
Legislation has been enacted for diseases which affect 
a far less percentage of the population, and from which 
the loss in national health and wealth is far less. Take, 
for instance, the laws controlling and limiting such 
diseases as phosphorus-poisoning, lead-poisoning, pro- 
hibitions on the sale of alcohol and opium. But the 
effects of these are obvious, and therefore have secured 
attention and a large measure of suppression. 

Legislation is demanded upon economic grounds. It 
must be perfectly obvious that any disease or factor 
which deleteriously affects the majority of the workers 
and wealth-producers of a nation is one which demands 
the serious consideration of legislators. 

At the very lowest estimate, the annual economic loss 
in Great Britain alone from this cause cannot be less than 
a million and a half sterling. This is based upon the 
assumption that the average extent of caries is three 
teeth per individual, and that each of these teeth 
causes one hour's loss of time and work per annum, and 


that the average value of this time is as low as threepence 
per hour. This works out at a sum of £1,687,500, 
taking the population at 45,000,000. As a matter of 
fact, the real sum must be far in excess of this, taking 
into consideration the prolonged economic loss incurred 
by the secondary occurrences of malignant disease, 
tubercular glands, pernicious anaemias, cerebral dis- 
orders, and the chronic debility mentioned above. The 
fact, also, that many of the people so afflicted become 
a positive charge on the community by occupying space, 
time, and attention in hospitals, workhouses, and asylums, 
tends further to increase the national loss. 

There can be no doubt whatever that a very large 
proportion of the cases occupying the beds and attending 
the out-patient departments of our general hospitals 
are there solely because of primary dental disease, which 
has led to grave secondary disorders. The recovery, also, 
of many patients suffering from a number of diseases 
having other than a dental origin is seriously hindered 
and prolonged by the presence of a septic mouth. 
Especially in this respect are thousands of pounds 
wasted annually in the sanatorium treatment of phthisical 
patients, who either cannot masticate properly the food 
abundantly supplied, or in whose mouth it becomes incor- 
porated with a quantity of septic and toxic material, the 
constant ingestion of which either prevents or con- 
siderably retards recovery. 

The Form of Legislation. 

It has been amply demonstrated that the prevalence 
of caries is due to the habitual consumption of " arti- 
ficial " as opposed to " natural," articles of diet. Most of 
the forms in which starchy and sugary foods are taken 
at the present time can only be regarded as luxuries, 
and, moreover, as dangerous luxuries — at least as dan- 
gerous as alcohol, for instance ; and, like alcohol, they 
should be taxed. The manufacture of sweetmeats, 


confectionery, and fine white flour, should be carried 
on only in bond ; and all such articles should be subject 
to Excise, either when manufactured at home or im- 
ported from elsewhere. The amount of the taxation 
should be sufficient to appreciably diminish the demand 
for such commodities, and the moneys so collected should 
be applied to the cheapening of other equally nutritious 
and less harmful forms of food — not less harmful only, 
but actually preventive of dental disease. Particularly 
the culture, carriage, freight, and importation, of fruit 
and fresh vegetables (and of meat in some places) should 
be fostered and aided, so that such articles may come 
(especially fruit) to be regarded as common, ordinary, 
and necessary constituents of every meal, instead of being, 
as at present, regarded as unnecessary and too expensive 
for common and constant use. Such legislation might 
well accord with a " back to the land " or " closer settle- 
ment " policy, the desirability of which, on economic 
grounds, is so much advocated. 

In addition, the preventive treatment of dental caries 
must be made one of the most important branches of the 
public health service. To initiate and organize a depart- 
ment to deal efficiently with this branch alone, would be a 
source of national economy. 

The present system of inspection and advice is good 
and necessary, and is a step in the right direction ; but 
by itself it is futile, and almost useless to stem the tide 
of this national disease. The proposed system of 
treatment by means of fillings and extractions on the 
most extensive and costly scale can hardly be much 
better ; it is to be regarded as a policy of expediency 
rather than of principle. No universal method of treat- 
ing disease can be recognized as being upon right lines ; 
no enormous expenditure of public money for the treat- 
ment of disease can be justified unless that treatment 
strikes at the cause of the trouble, and gives some reason- 
able hope that the incidence of the disease will be 
materially lessened. If the simile may be pardoned, such 


schemes are as if an army of small boys were pelting a 
glass house with stones, and the owners, instead of at- 
tacking and dispersing the cause of the trouble, employed 
an equally large army of workmen to be constantly 
repairing the damage as it went on. There would be 
two inevitable results: the vigour and number of the 
attackers would increase daily, and the work of the 
workmen would deteriorate. 

There is but one rational way of treating disease on 
a large scale— -that is, by building up the resistance, 
active and passive, of the individual to the disease, 
and by removing any obvious source of disease. How 
this may be done in the case of dental caries we have 
already considered in detail, and it is along such lines 
that State intervention seems to be required. The 
national health demands legislation. The pain and 
suffering, the lowered mental and physical condition, of 
the little children cry aloud for help. The people, their 
parents, are for the most part blind and ignorant as to 
the cause and remedy. For the removal of this ignorance, 
for placing means for combating the disease within the 
reach of all, and for making disease-causing factors less 
accessible, the State must be responsible 


Abyssinians, food of, 260 
Aceto-acetic acid, 172 
Acid, citric, 144 

dietaries, 147, 276 

drinks, 279 

-forming bacteria, 20 

hydrochloric, 108 

lactic, 105 

mouth-washes, 229, 232 

potassium tartrate, 143, 

potential diets, 215 

sodium phosphate, 104 

tannic, 143 

tartaric, 144 
Acidity of foodstuffs, 210, 276 
Acids, effect of, on enamel, 104 

natural organic, 195 
Adenoids, secondary, 40 
Adsorption, 95 
Africa, natural races of, 259 
African teeth, 12 
Age influences, 15 
Albumin in saliva, 1 1 1 
Alcohol, 217 
Ale, 145 
Alkaline dentifrices, 152, 226 

potential of diets, 2 1 5 

-producing bacteria, 235 
Alkalinity index, 134 

of foodstuffs, 210 
Amasa, Kaffir, 260 
Ameloblasts , 73 

Ammonia, 193 
Anglo-Saxon skulls, 1 1 
Antibiosis, 234 
Antiseptics, use of, 216 

objections to, 220 
Apotheosis of mechanical pro 

phylaxis, 225 
Apparatus, odontograph, 61 

saliva segregator, 133 

sclerometer, 10 1 
Arabian medicine, 3 
Armenian teeth, 12 
Arrested caries, xvi, 50 

possible at enamel 
surface only, 50 
Artifact lines, 67 
Asiatic teeth, 12 
Attrition, extreme, ^$ 

in native races, 267 
Australian aborigines, 261 

teeth, 12 

Bacteria, acid -forming, 20 
inoculation with, 234 

Bacterial plaques, 2 1 

Benzoic acid, 219 

Beverages for children, 279 

Bibliographies, 8, 17, 59, 268 

Bilberries, 253 

Bile acids, 193 

pigments, 193 

Biwa fruit, 263 

Black Club methods, 225 




Blastomycetes, 236 
Bread, aeration of, 272 

fruit, 255 

home-made, 271 

leavening, 272 
British Central Africa, natives 

of, 259 
British skulls, 1 1 
Bronze Age skulls, 1 1 
Brushing of teeth, 223 
Bulrush root, 261 
Burmese teeth, 12 
Bushmen, 260 

Calcarine fissures, 84 
Calcium magnesium balance, 

phosphate, 1 1 1 
Calcoglobulin, 112 
Calculus, and oral sepsis, 233 
Cannabis indica, 259 
Cannibalism, 247 
Carbohydrates : 

debris, 242 

experiments, 240 

factor, 199 

followed by acids, 2 1 1 

organisms destructive of 
carbohydrate debris, 236 

summary, 215 
Carbon dioxide solution, 109 

content of saliva, 233 

dispersion of carbohydrate 
debris, 242 
Caries, arrested, xvi, 50 

at enamel surface only, 

increase in, xv, 1 1 
Cassava, 258, 266 
Central American teeth, 12 
Chairs of research work, 291 
Chemical composition of en- 
amel, 1 17 

theory of caries, 18 
Chemico-parasitic theory, 19 
Children and hard food, 31 

Children, correct diet, 276 
drinks, 279 

tooth-cleaning, 220 
Chinese dietary, 263 

teeth, 12 

tooth-paste, 1 
Chinwans of Formosa, 255 
Chlorides, 179 

table, 180 
Cider, 271, 280 
Citric acid, 144 
Civilization and caries, 14 

modern, dietaries of, 269 
Cocaine on tongue, 153 
" Comforter "-sucking, 34 
Comparison of carious teeth in 

modern races, 12 
Confectionery, 271 

to be taxed, 296 
Cooking-classes, 286 
Corynocarpus Icevigata, 249 
Cranberries, 253 
" Crowding " and caries, 27 
Curvature of enamel surface, 57 
Cyttaria Darwinii, 254 

Decalcification of enamel, 206 
Deciduous teeth, condition of, 
odontograms, 64 
Density, comparative, 98 
degree of, 101 
estimated in mercury, 97 
of enamel, 96 
of Maori teeth, 100 
Dental Association, British, 
preservation of the teeth, 7 
Dental caries and heredity, 27, 
incidence of, 9 
pathology of, 1 8 
source of oral sepsis, 24 
statistics, 10 
theories of, 18 
Department of Public 
Health, suggested, 296 



Dental detergents, 165, 275 
disease, results of, 293 
prophylaxis and diet, 276 
students and drinks, 279, 
Dentifrices, 2 

action of, 151 

alkaline, to be abandoned, 

chalk, 5 
use of, 226 
Dentistry, preventive, 290 
Dentists and teaching, 289 
Departures from the normal, 

Diagrams in lectures, 285 
Dialysis of saliva, 188 
Diarrhoea, cause of, 278 
Diet : caries-immune races, 247 
fibrous, 32 
of civilization, 29 
of school-children, 272 
softness of modern, 269 
Dietaries, English, 156 
acid, 147 
insipid, 270 

of modern civilization, 269 
of Old England, 271 
suggested, 277 
Diseases and dental caries, 292 
Disposition of teeth, factors 

influencing, 27, 34 
Dissected jaws, child, 35 
Dog's teeth, odontogram, 65 
Driffield Collection of Skulls, 

1 1 
Dummy teats, 34 
Durian fruit, 257 
Dutch tooth-powder, 4 

Early Iron Age, skulls, 1 1 
Ebers papyrus, 1 
Educational measures, 283 
Egyptian dentistry, 1 

teeth, 12 
Electrical theory of caries, 18 



Enamel, chemical composition 
of, 117 
decalcification of, 
density of, 96 
effect of acids on, 
elephants', 117 
native teeth, 79 
normal, departures from, 

of civilized teeth, 80 
opaque spots, 88 
pathological fissures,. 84 
physical properties of, 90 
rehardening of , 113 
resistance of, 27 
solubility of, 104 

in acid sodium phos- 
phate, 104 
in carbon dioxide so- 
lution, 109 
in hydrochloric acid, 

in lactic acid, 105 
in orange-juice, 107 
strength of, 31 
striation in, 71 
surface, 49 

arrest of caries at, 50 
curvature of, 57 
fissures, 84 
hardness of, 10 1 
histological examina- 
tion of, 5 1 
in outline, 54 
permeability .of, 90 
thickness of, 3 1 
Environment, 43 
Epithelial debris, 191 
Equations, chemical, 20 
Esquimaux, 12 

dietary, 253 
Ethylidene lactic acid, 200 
Experimental evidence, ani- 
mals, 156 
Extirpation of the salivary 
glands, 165 



Fauces, muscles of, 35 

Feeding-bottles, 38 

Fern-root, 248 

Ferric chloride test, 171 

Fifteenth-century medicine. 3 

Figs and the teeth. 2 

Fijians, 254 

Finger-sucking, 34 

Fissures in enamel, 84 

Flour, fine white, to be taxed, 

Food, last eaten. 274 

softened and neutralized. 
Foodstuffs, acidity of , 210 

alkalinity of, 210 
Forces of natural protection, 
active. 123 
passive. 47 
Formalin, 217 
Formic aldehyde, 218 
Formulae, acid mouth-wash, 

Fruit for children, 2j^ 

a chief article of food, 
native races, 247 et seq. 
Fruits, tinned, 279 
Fuchsia excorticata, 249 
Fuegians, 254 

Function of Nasmyth's mem- 
brane, 1 1 1 
of nerves of taste, 127 

Glands, salivary, 12S, 157 
Glucose, 193, 238 
Glycogen, 193 
Gold encasement, 225 
Gnatho-dynamometer, 31 
Grape cure, 280 
Graphite staining method, 80 
Greek medicine, 1 
Guachos, 266 
Guanches' teeth, 12 
Gum-chewing, Maori. 251 
Gustatory stimuli, elimination, 

Hard foods, 31 

Hardness of enamel surface, 

measuring, 10 1 
Heredity and dental caries, 27, 

Hereros, 260 
Hindoo teeth, 12 

dietaries, 262 
Histological examination of 

enamel, 5 1 
Honey, 271 
Hue, 249 
Hustling age, 32 
Hydrochloric acid, 108 
Hydrogen dioxide, 217 

peroxide, 218 
Hyphomycetes, 235 
Hypoplastic teeth, 88 
Hypothesis of cause of permea- 
bility, no 

of imbrication lines, jt, 

Imbrication lines, 12, 67, y$ 
definition of, 69 
hypothesis of, "Ji 

Immune bodies, 189 

Immunity and mouth organ- 
isms, 243 

Incidence of caries, summary, 

Index, alkalinity, etc., 134 
India, inhabitants of, 262 
Indians, Central American, 258 
Guiana, 256 
New Mexican, 258 
North American, 257 
North - West American 
Coast, 254 
Inoculation with other organ- 
isms, 234 
In salivation, effect of, 202 
Insipid dietaries, 270 
Inspection, school, 296 
Ipomcea chrysorrhiza, 248 
Isomaltose, 193 



Jakun peoples, 2~ : j 
Japanese dietarv, 263 

teeth, 12 
Jaws, effect of soft foods on. 2j 

Kabyles, 260 
Kaffirs, 260 

tooth-cleaning, 221 
Kaki fruit, 263 
Karaka, 249 
Karengo, 249 
Kauri-gum. 212 
Kava. 2- : ' : 
Kumara. 248, 256 
Kutukutu, 249 

Lactic acid, solubility of enamel 
in, 105, 1 14 
ethylidene, 200 
fermentation, 20 

fermentation in vitro, 200 

in saliva. 193 

insalivation. 202 
Lapps' dietary, 253 
Leavening bread, 272 
Lectures to teachers, 285 
Legislation, form of, 295 

need for, 292 

on economic grounds, 294 
Lemons, 139, 281 
Leucine, 193 
Lilium colambianiim, 258 
Lip-sucking, 34 
Liquids, effects of, on saliva.. 

Lodgeability, 207 

and fibrous matter, 209 
LysoL 217 

Maize, 2 $8 

Malacotic teeth, 50, 80 

odontograms, 62 
Malays, 256 
Malay teeth, 12 
Maltone, 193 
Manganga, 259 

Manioc, 258 
Maori bird:- 2 

cooking, 250 

dietary, summary. 251 

food, 248 


fish, 250 

immunity due to salivary 

stimulants. 2^,3 
race, 247 
skulls. 1 1 

teeth, 13, 91, 93, ioo, 105. 
odontograms, 63 
Mastication, effect of, 28 
Masticatones. Indian. 254 

Maori. 251 
Mechanical prophylaxis, apo- 
theosis of, 225 
Medical practitioners, 28/ 

and dental prophvlaxis, 
Melanesians, 254 
Mercuric chloride, 218 
Mesenteric organisms. 23? 
Messalina's dentifrice, 2 
Methyl orange, 135 
Mett's tubes, 162 
Mohwa fruit, 262 
Moors of Morocco, 260 
Mouth-breathing, 41 

washes, antiseptic, 217 

alkaline to be aban- 
doned, 226 
acid, formulae, 229 
Mucin, 134, 181 

acid precipitation of, 182 
Mucinometer, 185 

Nardoo, 261 

Narrowed dental arches. 41 
Nasal cavity, narrowing of, 41 
Nasmvth's membrane, 23. no, 

Native races, attrition of teeth, 




Native dietaries, 247, 253 

teeth, 50 

lustrous, 79 
Need for special legislation, 

Negative hereditary force, 45 
Negroes of West Africa, 260 
Nerve, auriculo -temporal, 128 

chorda tympani, 128 

glosso-pharyngeal, 126 

lingual, 127 

sympathetic, 128 
New Mexicans, 258 
Nipple, normal, $7 
Normal, the significance of 
departures from, 79 

Oceanians, 254 
Odontograms, 62 
Odontograph, 60 
Opsonins, 190 

Oral hygiene, lessons in, 284 
Oral sepsis and calculus, 223 
from dental caries, 24 
other sources, 25 
Orange-juice, 107 
Oxygenetic factors, 199 

Pain, stimulus of, on saliva, 

Paiwari, 256 
Palm, mariba, 258 

carnahuba, 258 
Pandanus fruit, 261 
Papuans, 256 
Parotid secretion, 136 
Pathological significance of ab- 
normalities, 79 
fissures, 84 
opaque spots, 88 
Pathology of dental caries, 

Percentage of carious teeth, 

Permeability experiments, 90 
degree of, 91 

Persian dietary, 263 
Phagocytosis, 191 
Pharynx, muscles of, 35 
Phenolphthalein, 135 
Phosphates, 177 
Physical Deterioration Com- 
mittee, 10 
Physical properties of enamel 
surface, 90 

conclusions, 115 
Pilocarpine, 173 
Piper methysticum, 255 
Plaques, 182 
Poi, 255 

Polynesian teeth, 12, 254 
Poporo, 249 
Poroporo, 249 
Porosity compactness, 96 
Port wine, 145 

Potassium sulphocyanate, 
origin of, 175 
table, 173 

tartrate, acid, 227 
Prehistoric crania, 12 
Prevalence of caries, increase, 

1 1 
Prisms of enamel surface, 71, 

Prophylaxis, mechanical, apo- 
theosis of, 225 

and meals, 276 

in textbooks, 290 
Protein and carbohydrate mix- 
ture, 205 
Psychical secretion, saliva, 128 

depression, 155 
Pteris aquilina, 248 

escidenta, 248 
Ptyalin, 134, 160, 193 

effect of acid on, 164 
Pycnometer, 97 
Pygmies of Central Africa, 260 
Pyorrhoea alveolaris, 25, 237 
Pyrethrum, 186 

Quinoa, 258 



Rabbits, experiments on, 156, 
hardness of teeth, 121 

Racial incidence of dental 
caries, 9 

Reduction of oxygenetic fac- 
tors, 199, 216 

Rehardening enamel, 113 

Research work, 291 

Resistance of enamel, 27 

greater, of lower teeth, 17 

Retzius, striae of, 67 

Roman toothpicks, 2 

Romano-British skulls, 1 1 

Royal Commission on Physical 
Deterioration, 294 

Saccharomycetes, 237 
Sacchavomyces albicans, 237 

coagulatus, 238 

experiments with, 240 
Sago, 255 
Sakai tribes, 257 
Salads, 277 
Salicylic acid, 219 
Saliva, 125 

abnormal constituents of, 

alkalinity of, 104, 135, 

amount of, 135 
collection of, 131 
composition of, 133 
conclusions, 194 
dialysis of, 189 

effect of acids, 188 
of alkalies, 188 
during acid diet, 147 
effect of dentifrices, 151 

of liquids, 145 
flow of, 1 34 
immune bodies in, 189 
methods of obtaining, 129 

during mastication, 

of snake-charmers, 189 

Saliva, proteids in, 104 
reflex arc, 127 
" resting," 136 
" rinsing," effects of, 130 
ropy, 183 
secretion of, normal, 126 

psychical, 128 
segregator for, 133 
stimulation of, in masti- 
cation, 131 et seq. 
otherwise, 186 
tables, 136 
taste stimuli, 140 
Salivary depressants, 138, 141, 
150, 155, 211 
excitants, 138, 141, 155, 

21 1 
glands, extirpation of, 165 
stimulants, 131 et seq., 
Samoyedes, 253 
Sapidity, importance of, 265 
Schleswig-Holstein Dental As- 
sociation, 10 
School-children, diet of, 272 
Schreger's lines, 55, 67 
Sclerometer, 10 1 
Sclerotic teeth, 50, 81, 83 
odontogram, 64 
Secretion of saliva, normal, con- 
ditions of, 126 
psychical, 128 
variations due to 
taste stimuli, 140 
Sedentary life, 32 
Segregator for saliva, 133 
Semang tribes, 256 
Septic theory of dental caries, 

Septicaemia, chronic, 292 
Sexual influences, 1 5 
Sicilian teeth, 140, 281 
Silver nitrate stain, 90 
nature of, 94 
Sinuous fissures, 84 
Sixteenth-century medicine, 3 



Skiagram of jaws, boy of six, 
child, 36 
Snake-charmers, saliva of, 189 
Sodium carbonate, 143 

phosphate, acid, 104 
Soft foods, effect of, 27 
Softness of modern diets, 

Solarium aviculore, 249 

nigrum, 249 
Solubility of enamel, 104 

depends on total amount 
of acid, 106 

qualitative, 105 

quantitative, 108 
Sour fruit, 270 
Soured milk treatment, 281 
South American teeth, 12 
Stain, silver nitrate, 90 
Staining method, graphite, 8r 
Staphylococcus cerevisice, 240 

viscosus, 239 
Starches and sugars never to 

be taken alone, 2 1 5 
Statistics, dental, 10 
Stellate reticulum, no 
Stick tooth-cleaner, 221 
Stomatology, 289 
Stone Age skulls, 1 1 
Strawberry, 258 
Striae of Retzius, 67, 69 
Striation in enamel, 71 
Sublingual secretion, 136 
Submaxillary secretion, 136 
Sucking habits, 34 
Sugar, 214 

danger of, 185, 280 

fermentability of, 202 
Sulphocyanate of potassium, 
internal administra- 
tion of, 173 
origin of, 175 
Suppurative dental arthritis, 

Susceptibility of different 

teeth, 16 
Sweetmeats to be avoided, 
should be taxed, 296 
Sweet potato, 248 

Taboos, 266 
Tannic acid, 143 
Taro, 263 

flour, 255 
Tartar, 4 
Tartaric acid, 144 
Tasmanian aborigines, 261 
Taste perception, 153 

stimuli, 140 
" Tastes " of a child, 270 
Tax on sweetmeats, 296 
Teachers, lectures to, 285 

of cooking, 286 

primary schools, 283 
Tea-drinking, 271 

effects of.. 143, 145 

evils of, 278 
Teat, natural-shaped, t,j 
Teeth, disposition of, 2j , 34 

empirical classification of, 

tables showing degree of 
permeability, 91, 93 
Theories of dental caries, 18 
Thymol, 219 

Tierra del Fuego, teeth, 12 
Time experiments with carbo- 
hydrates, 240 
Ti-tree root, 249 
Todas, diet of, 262 
Tooth-brush, use of, 221 
Tooth-paste, Chinese, 1 

Egyptian, 1 
Toothpicks, Roman, 2 

Saxon, 2 
Tooth-powder, Dutch, 4 
Tooth-sticks, 221 
Totemism, 266 
" Tough " food, 30 



Tutin - - 
Tutu-berry _ 4 

Uganda, natives of, 25 
Upper teeth, increased sus- 
ceptibility of. 1 7 

Urea. 193 

Varietv in food, importance of, 

- ■ 

: _ - 

irian diet, predominant 
among native races, 247^/ seq. 

r drinking, importance 
of salts in. 1 19 
Whisky. 145 
Wine, effect of. 145 27] 
Worm theory, caries, 18 

Yams. 261 

Yeast, iermc-ntatior. by, 236 


(Bibliographical references in thick type.) 

Abbott, 18 
Aristotle, 2, 6 
Austin, 90 
Avicenna, 3 

Bancroft, 268 
Barr, J. Stoddart, 

Beach, 169, 176 
Bell, 4 
Berdmore, Thomas, 

Bessenge, R., 217 
Bibra, von, 1 17 
Bidder, 157 
Black, G. V., 21,31, 

50, 59, 281 
Blagden, 268 
Borisov, 162 
Bridgeman, 18 
Brown, J. M„ 268 
Bunge, 1 19, 280 
Bunon, 4 
Bunting, 171 

Cannon, 160 
Carlson, 194 
Celsus, 2 
Chassevant, 220 
Chouppe, 169 
Colyer, 40, 136 
Cook, 181 

Crooke, 268 

Cunningham, 10, 
12, 15, 17 

Darwin, 254 
Densham, 8 
del, 126 

Ellenberger, 168, 

Fauchard, Pierre, 4 
Favre, 2^7 
Fehr, 165 
Fenwick, 175 
Fitchett, F., 252 
Florian, 169 
Floxas, 218 
Foreest, of Leyden, 3 
Fox, 5, 8, 18 
Frerichs, 168 

Gabell, 90 
Galen, 18 
Gamgee, 193 
Gassmann, 117 
Geyger, of Leipsig, 

169, 173 
Gillen, 268 
Giovanna, of Arcoli, 

Goadby, 202, 235, 

Goddard, 5, 8 
Greve, 15, 17 
Guerini, 8 
Guppy, 255, 268 

Haddon, 268 
Haidenhain, 150, 

Halliburton, 168, 
Harden, 238 [193 
Harris, ;, 8, 19 
Head, 104, 113 
Hecht, 169 
Henderson, 8 
Hill-Tout, 268 
Hippocrates, 2, 18 
Hitchcock, 17 
Hoffmeister, 168, 

Hoppe-Seyler, 95, 

Ho witt, A. \\\, 268 
Hugenschmidt, 169 
Hunt, 218, 230 
Hunter, 4, 18 
Hutchinson, R., 280 

Jacubiowitsch, 168 
Johnson, 181 
Junker, of Halle, 4 




Kenwood, 122 
Kirk, E. C, 51, 59, 

169, 182 
Kjellmann, 253 
Kolliker, 69 
Kiilz, 110 

Langley, J. N., 131, 

Layton, 10, 17 
Lloyd, A. B., 268 
Logan, 257 
Low, 169, 176 

Mackenzie, 40 
Magitot, 9, 15, 17 
Malcolm, 120 
Mayer, A., 238 
Mayer-Tidy, 175 
Meakin, 268 
Michaels, 193 
Michel, of Wurz- 

burg, 168, 176 
Miller, 6, 19, 49, 59, 

126, 169, 189, 

219, 237, 264 
Milles, 19 
Minkowski, 165 
Mitscherlich, 168 
Moore, B., 165, 168 
Morris, G. H., 238 
Mummery, J. R., 9, | 

11, 17, 247, 257 

Munk, 168 
Muntz, 169 

Nuck, Anton, 4 

Oehl, 168 
Oppenheim, 169 
Osier, 294 
Ottofy, 12, 17 

Parkes, 122 
Pasteur, 6 
Patrick, 12, 17, 264 
Paul, of .-Egina, 2 
Pavlov, 126, 143, 

155, 162 
Pliny, 2 
Pratt, 268 

Ratzel, 253, 257, 

265, 268 
Richards, F. W., 10, 

15- 17 
Richet, 220 
Rigolet, 126 
Rivers, 268 
Riviere, 3 
Robertson, Aitchi- 

son, 10, 17, 202 
Rose, of Munich, 7, 

10, 15, 17, 119 
Ryan, 194 

Schafer, 131, 165, 

Schmidt, 168 
Schiitz, 162 
Seligmann, 268 
Sellheim, 129 

Skeat, 257, 268 
Smale, 136 
Smith, D. D., 224 
Smith, Hopewell, 

49, 59 
Soemering, 175 
Spencer, 268 
Starling, 127 

Taylor, 268 
Thomas, N.W., 268 
Tomes, Sir J., 19, 

Tomes, C. S., 49, 59 
Tregear, 268 

Underwood, 19 

Von Bibra, 117 

Wadsworth, 217 
Wagner, 168 
Walkoft, 69 
Wallace, 269, 284 
Waugh, 177 
Weiske, 120 
Werner, A., 268 
Westcott, 5, 18 
Westrumb, 175 
Williams, Leon, 21, 

49. 51. 59, 69, 

Wright, T., 2 
Wright, W., 17 

Young, 238 

Bailliere, Tindall ana Cox, S, Henrietta Street, C event Garden